QH 
431 
C265 


GENETIC  STUDIES  OF  RABBITS 
AND  RATS 


BY 

W.   E.   CASTLE 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
WASHINGTON,  MAY,  1922 


^GENETIC  STUDIES  OF  RABBITS 
AND  RATS 


BY 

W.  E.   CASTLE 
\> 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
WASHINGTON,  MAY,  1922 


BL* 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
PUBLICATION  No.  320 


Copies  of  this  book 

first  issued 
MAY  2  21922 


TECHNICAL    PRESS 
WASHINGTON,   D.   C. 


GENETIC  STUDIES  OF  RABBITS  AND  RATS. 


PART  I. 

SIZE-INHERITANCE  IN  RABBIT  CROSSES. 

In  the  last  fifteen  years  numerous  studies  have  been  made  of  the 
inheritance  of  characters  which  are  quantitatively  variable  or  fluc- 
tuating. As  a  result  of  these  studies  it  has  become  clear  that  in 
many  cases  fluctuation  is  due  to  non-genetic  causes,  to  the  environ- 
ment rather  than  to  the  constitution  of  the  germ-cells.  In  such 
cases  selection  is  without  effect  in  modifying  the  racial  character. 
This  is  the  accepted  explanation  of  the  negative  results  obtained  by 
Johannsen  in  selecting  beans  for  increased  or  decreased  size,  and  of 
the  similar  results  of  Ewing  in  selecting  plant-lice  for  altered  body 
dimensions,  and  those  of  Jennings  and  others  with  paramecium. 

But  in  a  majority  of  cases  variation  due  to  genetic  causes  occurs 
in  association  with  that  due  to  non-genetic  or  environmental  causes; 
in  fact,  it  is  possible  to  distinguish  between  the  two  only  by  the 
results  of  systematic  selection.  When  the  environment  is  kept 
constant  and  a  race  does  not  change  in  response  to  selection,  we 
assume  that  no  genetic  variation  is  present.  But  if  the  race  does 
change  in  response  to  selection,  we  have  no  alternative  but  to  assume 
that  the  variation  is  genetic  in  character.  Body-size  in  birds  and 
mammals  shows  well  the  simultaneous  yet  distinct  action  of  genetic 
and  non-genetic  agencies.  The  amount  and  quality  of  the  food 
supplied  to  an  animal  limits  its  size,  yet  if  food  is  supplied  in  abun- 
dance and  of  proper  quality,  some  races  of  animals  attain  greater 
size  than  others.  This  is  the  result  of  genetic  differences. 

The  analysis  of  such  genetic  differences  is  difficult.  A  pioneer 
attempt  was  made  by  Galton  (1889)  in  his  study  of  human  stature, 
the  inheritance  of  which  he  characterized  as  blending.  This  term 
was  adopted  by  Castle  et  al.  (1909)  in  describing  the  inheritance 
of  ear-length  and  body-size  in  rabbits.  A  Mendelian  interpretation 
of  size-inheritance  was  later  advocated  by  Lang  (1910),  based  on 
the  multiple-factor  hypothesis  of  Nilsson-Ehle  and  this  has  now 
received  general  acceptance.  Davenport  (1917)  has  recently  applied 
it  to  human  stature,  but  has  gone  a  step  farther  in  assuming  that 
the  genetic  factors  which  govern  size  in  one  part  of  the  body  are 
often  not  the  same  as  those  which  govern  the  size  of  other  parts. 

Punnett  and  Bailey  (1914,  1918)  in  their  studies  of  size-inheritance 
in  poultry  and  in  rabbits  bring  forward  a  different  hypothesis. 


4  -KTIC    STUDIES   OF   RABBITS   AND    RATS. 

They  attempt  to  explain  the  results  of  size-crosses  with  the  aid  of 
genetic  factors  affecting  the  size  of  all  parts,  but  relatively  few  in 
number,  a  different  potential  effect  on  size  being  assigned  to  each  of 
the  assumed  factors. 

With  a  view  to  throwing  further  light,  if  possible,  on  this  confused 
situation,  a  renewed  investigation  of  size-inheritance  in  rabbits 
was  undertaken  by  me  in  January,  1917.  To  clarify  the  matter,  it 
seemed  desirable  to  obtain  races  as  pure  as  possible  and  as  unlike  as 
possible  in  size,  to  breed  each  separately  and  study  its  variability 
and  at  the  same  time  and  under  similar  conditions  to  cross  the  same 
races  and  study  the  variability  of  the  FI  and  F2  generations  of  off- 
spring. For  this  purpose  two  small  races  of  rabbits  were  selected, 
Polish  and  Himalayan,  and  one  large  race,  that  of  the  Flemish  Giant. 
Stock  was  obtained  from  exhibitors  at  the  last  previous  Boston  show 
who  had  been  awarded  prizes  for  the  excellence  of  their  animals  in 
these  several  breeds. 

In  carrying  out  the  original  plan  to  study  size-variation  in  the 
uncrossed  races,  I  have  been  only  partiallysuccessful,  but  a  good 
series  of  cross-breds  has  been  secured  and  studied.  In  the  pure 
races  (plate  1)  the  number  of  adult  individuals  studied  was,  Polish 
23,  Himalayan  8,  Flemish  5.  Adult  cross-breds  have  been  produced 
as  follows:  Polish X Flemish,  F,  27,  F2  137;  Polish X Himalayan, 
F,  25,  F,  55;  Himalayan  X  Flemish,  F!  17,  F2  70.  The  total  number  of 
adult  individuals  studied  for  size-characters  in  this  investigation  is 
367.  The  characters  studied  are  weight,  ear-length,  and  the  fol- 
lowing bone  measurements:  (1)  skull  length,  (2)  skull  width  anterior 
to  orbit,  (3)  skull  width  posterior  to  orbit,  (4)  length  of  femur,  (5) 
length  of  tibia,  (6)  length  of  humerus. 

Weights  were  taken  at  intervals  of  about  two  weeks,  from  the 
time  of  weaning  to  the  attainment  of  full  growth.  As  animals  are 
apt  to  increase  in  weight  through  the  accumulation  of  fat  after  the 
cessation  of  general  growth,  the  adult  weight  of  an  animal  is  taken 
as  the  maximum  weight  attained  under  one  year  of  age.  Small 
races  of  rabbits  attain  maturity  earlier  than  large  ones.  For  example, 
Polish  rabbits  are  usually  full-grown  at  ten  months  of  age,  whereas 
Flemish  may  grow  slowly  after  they  are  one  year  old.  The  skeletal 
measurements  studied  are  based  for  the  most  part  on  animals  which 
had  attained  the  age  of  fourteen  months,  but  some  measurements 
have  been  used  of  younger  animals,  when  it  has  been  found  by  com- 
parison of  different  measurements  that  full  growth  had  probably 
been  attained.  Adult  ear-length  is  attained  much  earlier  than  full 
body-size.  Growth  of  ears  is  practically  completed  at  twenty  weeks 
of  age.  Accordingly,  it  has  been  possible  to  use  the  ear- measurements 
of  animals  which  died  before  they  attained  full  body-size,  and  so 
the  totals  for  ear-length  studies  are  greater  than  those  for  weight 


GENETIC   STUDIES   OF  RABBITS  AND   RATS.  O 

(which  is  supposed  to  be  complete  at  one  year)  or  for  bone- 
dimensions,  which  as  a  rule  are  based  on  specimens  fourteen  months 
old. 

GROWTH-CURVES  BASED  ON  WEIGHT. 

Most  of  the  rabbits  were  born  in  the  spring  and  summer  months, 
May  to  August  inclusive,  but  some  were  born  as  late  in  the  year  as 
November  and  a  few  in  the  early  part  of  December.  None  was  born 
in  the  months  January  to  March  inclusive.  The  young  were  usually 
weaned  when  one  month  old,  at  which  time  periodical  weighing  of 
the  animals  was  begun.  It  was  considered  very  desirable  to  raise  all 
the  individuals  born,  for  fear  that  if  small-sized  individuals  should 
succumb  in  competition  with  their  larger  brothers  and  sisters,  the 
statistical  conclusions  might  be  vitiated  thereby.  To  this  end,  free 
use  was  made  of  foster-mothers.  Young  under  a  week  old  may 
readily  be  transferred  from  the  nest  of  one  mother  to  that  of  another. 
In  only  one  case  have  I  known  a  mother  to  refuse  to  care  for  foster- 
children  substituted  for  her  own  of  like  age.  Of  course,  notwith- 
standing all  our  precautions,  many  young  rabbits  died  before  reaching 
maturity,  either  from  intestinal  troubles  in  hot  weather  or  from 
nasal  troubles  ("snuffles")  in  cold  weather.  But  a  careful  study  of 
our  records  indicates  that  there  was  no  differential  selection  in  favor 
either  of  large  or  of  small  rabbits  in  these  deaths.  The  young  rabbits 
were  supplied  with  an  abundance  of  suitable  food,  in  summer  grass 
and  oats,  in  winter  hay,  oats,  and  cabbage  or  carrots.  Occasionally 
a  rabbit  was  not  weaned  promptly  at  one  month  of  age.  If,  for 
example,  an  individual  seemed  feebler  than  its  fellows  at  weaning- 
time,  it  might  be  left  with  the  mother  a  week  or  two  longer.  Again, 
differences  in  size  were  often  observed  at  weaning-time  between 
litters  of  like  ancestry,  but  of  unlike  number  in  individuals.  If  a 
doe  nurses  six  young,  they  will  average  smaller  at  weaning  than  will 
young  of  similar  ancestry  nursed  by  two  mothers,  each  of  which 
divides  her  milk  among  three  young.  Fanciers  believe  that  this 
affects  the  ultimate  size  of  the  offspring.  They  think  that  the 
largest  rabbits  are  obtained  by  rearing  only  two  or  three  young  to  a 
litter  and  by  allowing  these  to  nurse  the  mother  for  six  weeks  or 
two  months.  Our  observations  do  not  support  this  view,  but  indicate 
that  the  ultimate  size  attained  is  influenced  very  little,  if  at  all, 
by  the  size  of  the  young  at  weaning,  provided  they  are  in  good  health 
and  growing  condition  and  are  thereafter  fed  abundantly. 

Figure  1  illustrates  the  matter  well.  Rabbits  2650  and  2834  were 
half-brothers.  They  had  the  same  pure  Flemish  father  and  their 
mothers  were  of  the  same  pure  Polish  stock.  Rabbit  2650  was 
weaned  at  29  days  of  age  and  grew  slowly  until  he  was  71  days  old, 
when  he  weighed  600  grams.  Rabbit  2834  was  raised  by  a  foster- 


a 


GENETIC   STUDIES   OF   RABBITS   AND    RATS. 


mother  alone,  receiving  all  her  milk  until  he  was  weaned  at  71  days 
old,  when  he  weighed  1,530  grams,  more  than  2.5  times  as  much  as 
his  half-brother  at  the  same  age.  Notwithstanding  this  handicap 
in  his  favor,  he  was  overtaken  in  size  by  his  early- weaned  half- 
brother  at  age  194  days,  and  was  surpassed  by  him  in  adult  weight 
by  about  150  grams.  The  bone  dimensions  of  the  two  rabbits  were 
very  similar,  with  a  slight  but  probably  not  significant  superiority 
in  favor  of  the  late-weaned  individual.  In  the  case  of  neither  rabbit 
does  the  growth-curve  show  any  interruption  of  healthy  growth. 
The  form  of  the  growth-curve  is  affected  by  the  superior  nutrition  of 
2834  during  his  first  2  months,  but  the  ultimate  size  attained  is  not 
influenced  thereby. 

Figure  1  also  shows  the  growth-curve  of  a  third  rabbit  (2578), 
half-brother  to  each  of  the  others  (2650  and  2834).     He  was  born 


160       210        340       270 
AGE. IN  DAYS 

Fio.  1.— Growth-curves  in  weight  of  three  Ft  rabbits  which  were  half-brothers,  all  having  the 
same  pure  Flemish  sire  but  each  having  a  different  pure  Polish  mother.  Male  2578 
wms  born  July  26,  1917;  male  2660  was  born  August  9,  1917;  male  2834  was  born  Decem- 
ber 7,  1917.  Note  that  the  rabbit  which  was  largest  as  an  adult  (2650)  was  smallest 
up  to  160  days  of  age,  whereas  the  rabbit  (2834)  which  was  much  the  heaviest  as  a 
young  rabbit  because  he  received  all  the  milk  of  a  foster-mother  up  to  weaning  at  71 
day.  of  age,  nevertheless  fell  below  2650  in  adult  weight. 

just  two  weeks  earlier  than  2650,  was  weaned  at  the  same  age  (29 
days),  but  was  slightly  heavier  at  weaning  and  held  the  lead  up  to 
age  144  days,  when  he  was  practically  full-grown.  His  ears  were 
then  of  maximum  length,  10.4  centimeters.  On  the  same  day 
[December  17)  the  younger  rabbit  (2650),  although  lighter  in 


GENETIC   STUDIES   OF   RABBITS   AND    RATS.  7 

weight,  had  longer  ears  (10.9  centimeters),  a  fact  which  foreshadows 
his  greater  adult  size.  He  kept  on  growing  after  passing  age  144 
days  and  ultimately  became  much  heavier.  His  bone-measurements 
were  also  greater,  except  in  one  instance,  femur-length,  which  was 
practically  the  same.  In  the  case  of  this  pair  of  half-brothers,  the 
environmental  conditions  were  substantially  identical.  They  were 
born  within  a  fortnight  of  each  other,  weaned  at  the  same  age, 
and  grew  up  under  the  same  seasonal  conditions  on  similar  food,  yet 
they  diverged  in  adult  weight,  bone-measurements,  and  ear-length 
more  than  the  pair  (2650  and  2834)  which  had  such  different  environ- 
mental conditions. 

From  facts  such  as  these,  it  is  believed  that  accidental  differences 
in  environment  (though  we  have  striven  to  avoid  them)  have  little 
to  do  with  the  size-differences  observed  among  our  rabbits.  On  the 
other  hand,  it  is  clear  that  our  purest  races  of  rabbits  are  not  perfectly 
homogeneous  genetically  as  regards  size,  since  with  the  most  carefully 
controlled  environment  size-differences  occur. 

Figure  2  shows  the  growth-curves  of  two  female  rabbits,  3099  and 
3100,  litter  mates  borne  by  the  same  pure  Himalayan  mother  to  the 


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FIG.  2. — Growth-curves  of  two 
FI  rabbits,  litter-mates  borne 
by  the  same  pure  Himalayan 
mother  to  the  same  pure 
Polish  sire,  and  kept  together 
in  the  same  pen  throughout 
their  growing-period.  Note 
difference  in  character  of  the 
growth-curves.  The  rabbit 
which  was  larger  at  weaning, 
matures  earlier  and  remains 
smaller  as  an  adult. 


10       2«0      Z70      300 


same  pure  Polish  sire.  Both  were  weaned  on  the  same  day  at  the 
age  28  days.  They  were  kept  together  in  the  same  pen  during 
subsequent  growth.  At  birth,  3099  was  the  larger  of  the  two  sisters 
and  maintained  her  superiority  for  about  four  months,  when  her 
growth-rate  began  to  slow  up,  while  that  of  her  sister,  3100,  kept  on 
steadily.  At  about  the  age  170  days  the  originally  smaller  rabbit 
surpassed  her  sister  in  size  and  held  this  relative  position  thereafter. 
In  every  bone  measurement  she  was  a  little  larger  than  her  sister, 
but  in  ear-length  they  differed  little,  the  smaller  rabbit  being  credited 
with  having  slightly  longer  ears. 

From  the  weight-records  made  for  each  rabbit  it  is  possible  to 
construct  a  growth-curve,  as  in  the  cases  just  discussed.  Such 
curves  have  been  plotted  for  each  pure-bred  and  each  FI  cross-bred 


s 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


rabbit  raised.  From  these  curves,  readings  have  been  taken  giving 
the  approximate  weight  of  the  individual  at  the  ages  of  30,  40,  60 
days,  and  so  on,  at  30-day  intervals,  to  the  age  360  days.  Combining 
the  weight  records  for  each  group  of  individuals,  an  average  growth- 
curve  is  obtained  for  the  group,  as  shown  in  figure  3. 

In  this  figure  it  is  indicated  that  Polish  rabbits  are  small  at  30 
days  of  age,  but  grow  with  fair  rapidity  until  about  180  days  old. 
Then  the  growth-rate  declines  and  growth  is  practically  ended  at  the 
age  210  days.  In  many  cases  the  weight  actually  decreases  again 
after  attaining  a  maximum  at  sexual  maturity,  or  shortly  thereafter, 
as  Punnett  (1918)  has  observed.  But  such  decline  is  not  invariable, 
and  it  may  result  from  a  variety  of  causes,  such  as  less  nutritious 


FIQ.  3. — Growth-curves  of  the 
three  races  of  rabbits,  Polish, 
Himalayan,  and  Flemish, 
and  of  the  groups  of  FI  hy- 
brids obtained  by  crossing 
the  three  pure  races.  The 
average  adult  weight  of  each 
group  of  Fj  hybrids  is  shown 
for  comparison  with  FI,  be- 
low which  it  falls  in  every 
case. 


AGE.  IN 


A  ft,  IN  UAY9 

food,  a  cold,  or  lactation  (in  females) .  When  normal  conditions  are 
restored,  the  weight  usually  rises  again  and  subsequent  accumulations 
of  fat  usually  carry  the  final  weight  above  the  puberty  maximum. 
In  plotting  the  growth-curves  the  maximum  weight  attained  in  the 
first  year  is  considered  as  persisting  thereafter.  This  will  account 
for  the  fact  that  the  plotted  average  curves  do  not  show  any  decline, 
even  though  the  weight-curves  of  individuals  would  in  many  cases 
do  so.  The  rabbits  that  show  increases  in  weight,  due  largely  to 
fattening  subsequent  to  puberty  (180  to  210  days),  will  explain  the 
fact  that  the  weight-curve  continues  to  rise  until  the  end  of  the  period 
plotted,  360  days. 

In  the  case  of  Himalayan  and  Flemish  rabbits,  the  weight  at  the 
age  30  days  is  greater  than  that  of  Polish  rabbits.  The  growth-rate 

uso  greater,  so  that  the  growth-curves  continue  to  diverge  more 
and  more,  one  from  another.  The  slowing  up  of  growth  at  puberty 


GENETIC   STUDIES   OF   RABBITS   AND    RATS.  9 

(180  to  210  days)  is  also  less  abrupt  and  the  increase  in  weight  sub- 
sequent to  puberty  is  greater.  The  average  weight  at  360  days  of 
Polish  rabbits  of  both  sexes  is  less  than  1,400  grams,  for  Himalayan 
rabbits  it  is  1,800  grams,  and  for  Flemish  it  is  over  3,200  grams. 

In  Polish  rabbits,  as  compared  with  other  and  larger  breeds,  the 
initial  weight  is  less,  the  growth-rate  less,  and  the  completion  of 
growth  comes  earlier.  All  these  phases  of  growth  combine  to  make 
the  ultimate  weight  smaller.  Comparison  of  the  growth-curves  of 
Polish  and  Flemish  brings  this  point  out  very  clearly.  The  Flemish 
curve  is  far  above  the  Polish  curve  at  the  outset  and  diverges  from  it 
increasingly  up  to  the  age  360  days.  The  Himalayan  growth  curve 
lies  everywhere  between  the  Polish  and  Flemish  curves,  but  is  much 
nearer  to  the  Polish.  In  form,  however,  it  is  more  like  the  Flemish 
curve,  in  that  growth  continues  longer  after  puberty. 

FI  rabbits  produced  by  crossing  Polish  with  Himalayan  have  a 
greater  initial  weight  than  either  pure  parent  race  and  grow  faster. 
At  puberty  (180  to  210  days)  the  FI  rabbits  surpass  Polish  by  over 
500  grams.  They  are  more  than  40  per  cent  heavier.  As  compared 
with  Himalayans  of  like  age,  they  are  more  than  20  per  cent  heavier. 
At  age  360  days,  the  FI  rabbits  are  45  per  cent  heavier  than  Polish, 
but  only  9  per  cent  heavier  than  Himalayan,  since  the  slower-growing 
Himalayans  have  lessened  the  superiority  which  the  FI  rabbits  showed 
at  puberty,  but  have  not  extinguished  it. 

F2  rabbits  from  this  cross,  obtained  by  mating  the  FI  rabbits, 
brother  with  sister  or  half-sister,  show  an  average  adult  weight  of 
1,632  grams,  which  is  intermediate  between  the  adult  weight  of 
Polish  and  Himalayan  rabbits,  the  races  originally  crossed,  being 
20  per  cent  heavier  than  Polish  and  10  per  cent  lighter  than  Hima- 
layan. The  superiority  in  size  of  the  FI  animals  is  a  purely  FI 
phenomenon,  as  we  shall  see.  It  never  persists  into  the  F2  generation. 
Its  existence  is  nevertheless  an  important  practical  consideration, 
which  makes  grading  and  the  crossing  of  breeds  highly  advantageous 
under  certain  circumstances. 

In  the  cross  of  Polish  with  Flemish  rabbits,  FI  is  in  size  well  above 
the  intermediate  between  the  parent  races,  another  illustration  of 
FI  vigor,  although  in  this  case  FI  does  not  surpass  the  larger  race  in 
size.  The  form  of  the  growth-curve  is  also  intermediate.  Maturity 
is  attained  early,  as  in  the  Polish  race,  but  the  practical  cessation  of 
growth  comes  later  than  in  the  Polish  race,  at  240  days  rather  than 
at  200.  The  adult  weight  of  the  FI  rabbits,  at  the  age  360  days, 
averaged  2,539  grams,  as  compared  with  3,240  for  Flemish  and 
1,359  for  Polish.  The  intermediate  would  be  2,300  grams,  which 
the  FI  group  surpasses  by  more  than  10  per  cent.  In  the  Himalayan- 
Polish  cross,  FI  surpassed  the  intermediate  by  over  20  per  cent,  and 
F8  surpassed  it  by  3  per  cent. 


10  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

In  the  Flemish-Polish  cross,  as  in  the  Himalayan-Polish  cross, 
F»  falls  below  F,  in  size.  It  is  found  to  be  2,128  grams  as  compared 
with  2,539  for  Fi.  It  is  even  less  than  the  intermediate,  2,300  grams, 
by  about  8  per  cent. 

In  the  Flemish-Himalayan  cross,  the  growth-curve  for  F!  is  very 
similar  in  form  to  the  curve  for  pure  Flemish.  There  is  a  gradual 
falling  in  the  growth-rate  at  about  210  days,  which  indicates  the 
usual  slowing-up  influence  of  puberty,  coming  about  a  month  later 
than  in  Polish  rabbits.  But  growth  continues  even  after  this  retard- 
ing influence  sets  in,  just  as  it  does  in  Flemish  rabbits.  The  weight 
at  360  days  is  2,781  grams  as  compared  with  a  strict  intermediate 
between  the  parent  races  of  2,523  grams,  which  it  surpasses  by  10 
per  cent,  about  the  same  relation  found  in  the  Polish-Flemish  cross. 
Again  F«  shows  a  falling  off  as  compared  with  FI  to  2,466  grams, 
which  is  2  per  cent  less  than  the  intermediate. 

To  summarize  the  foregoing  observations: 

(1)  In  races  of  small-sized  rabbits  the  initial  weight  is  small,  the 
growth-rate    is    low,    and    growth    terminates    early.     Conversely, 
rabbits  of  large-sized  races  have  a  large  initial  weight  and  growth 
energy,  which  not  only  makes  them  grow  faster,  but  also  makes 
them  grow  a  longer  time  than  do  rabbits  of  small-sized  races. 

(2)  When  races  of  small  rabbits  are  crossed  with  a  race  of  large 
rabbits,  the  initial  weight,  growth  energy,  and  duration  of  growth 
are  all  intermediate  in  character,  but  are  greater  than  the  strict 
intermediate  in  the  Fi  generation  and  approximate  it  or  fall  slightly 
below  it  in  Fj. 

(3)  When  two  races  of  rabbits  (such  as  Polish  and  Himalayan)  are 
crossed,  which  do  not  differ  greatly  in  size,  FI  may  surpass  either 
parental  race  in  vigor  of  growth,  though  not  in  duration  of  growth. 
Consequently  the  maximum  advantage  in  size  of  FI  over  the  parent 
races  will  be  attained  at  puberty.     F»  will  approximate  the  interme- 
diate in  size  between  the  parent  races  originally  crossed. 

WEIGHT  AND  SEX. 

In  the  foregoing  pages  the  average  weight  of  groups  of  individuals 
has  been  under  discussion  without  reference  to  individual  variation 
within  each  group  or  the  effect  of  crossing  on  such  variation,  or  the 
relation  of  weight  to  sex.  In  any  discussion  of  the  inheritance  of 
weight,  these  questions  must  be  taken  into  consideration.  First 
let  us  consider  the  relation  of  weight  to  sex.  The  "standards"  of 
the  various  breeds  of  rabbits  formulated  by  breeders  in  England  and 
the  United  States  make  no  specification  as  to  the  relative  sizes  of 
the  two  sexes  in  the  small  breeds  of  rabbits,  but  in  the  large  breeds 
they  regularly  specify  a  larger  size  for  females  than  for  males.  Thus, 
the  English  standard  for  the  variety  Steel  Gray  Flemish  Giant 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


11 


(plate  1,  F)  specifies  "  Bucks  shall  be  not  less  than  11  pounds  and 
does  not  less  than  13  pounds."  An  American  publication  gives  the 
standard  weight  for  Japanese  rabbits  as  "bucks  7  pounds,  does  8 
pounds,"  that  of  French  Silvers  as  "bucks,  9  pounds;  does,  10  pounds 
or  over." 

The  existence  of  such  specifications  in  breed  standards  implies 
that,  at  least  in  large  races  of  rabbits,  the  female  either  is  naturally 
larger  than  the  male  of  like  genetic  constitution,  except  as  to  sex,  or 
else  that  the  breeders  have  some  expectation  of  making  it  so. 

The  relative  weight  of  the  two  sexes  in  the  groups  of  rabbits  which 
I  have  studied  is  shown  in  table  2.  In  the  Polish  breed,  males  were 
found  to  be  slightly  heavier  than  females.  The  single  male  Himalayan 
studied  differed  very  little  from  the  average  of  the  5  females;  but  in 
the  cross-bred  rabbits  of  all  three  combinations,  viz,  Polish-Hima- 
layan, Polish-Flemish,  and  Himalayan-Flemish,  females  were  heavier 
by  from  50  to  200  grams  (2.5  to  7.5  per  cent)  than  were  males  derived 
from  the  same  cross.  It  seems  clear,  therefore,  that  the  breed  stan- 
dards are  correct  in  recognizing  the  greater  weight  of  females  than 
of  males,  at  least  in  the  heavier  breeds  of  rabbits.  The  difference  is  a 
natural  one,  not  arbitrary,  but  the  amount  of  the  difference  has 
probably  been  exaggerated  in  the  standards,  which  call  for  a  difference 
of  about  15  per  cent.  This  is  double  the  greatest  difference  observed 
by  me. 

INHERITANCE  OF  WEIGHT. 


Individual  variation  in  weight  can 
methods.     Maximal  first-year  weight 
the  few  cases  of  rabbits  received  as 
adults.     For  the  present,  the  slight 
difference  in  size  of  the  two  sexes 
will   be   disregarded.     The   general 
character  of  the  variation  in  weight 
is  presented  graphically  in  figures  4 
to  6.    The  data  on  which  these  graphs 
are  based  will  be  found  in  table  3. 

Figure  4  shows  that  the  modal 
weight  of  Polish  rabbits  is  about 
1,400  grams,  while  Himalayan  rab- 
bits are  about  400  or  500  grams 
heavier.  The  Fi  cross-breds  are 
heavier  than  either  pure  race,  as 
shown  also  in  the  growth-curves  (fig. 
3) .  They  vary  symmetrically  around 
the  class  whose  center  is  1,949  grams, 
designated  class  19  in  figure  4.  The 
Fj  generation,  which  contained  just 


best  be  studied  by  statistical 
will  be  dealt  with,  except  in 


NO. 


F^.PXH 


F..PXH 


H 

nri    P^3 


10  II   12  13  UVI5  16  17  18  I9ZOZI  ZZ  23  24 
WEIGHT,  IN  HEKTOGRAMS 

Fia.  4. — Polygons  showing  variation  in 
weight  of  pure  Polish  (P)  and  pure 
Himalayan  (H)  rabbits,  and  of  their 
Fi  and  Ft  hybrid  offspring. 

twice  as  many  individuals  as 


12 


GENETIC   STUDIES   OF   RABBITS   AND    RATS. 


Fi,  varies  about  class  16  as  a  mode,  being  about  300  grams  lighter 
in  average  weight  than  the  Fi  groups.  The  variability  of  this  group 
as  measured  by  the  standard  deviation  is  only  slightly  greater  than 
that  of  FI,  being  233  grams  as  compared  with  218  grams  for  Fi. 


20- 


14- 

rt- 


F,,PXF 


..EL 


1 12  13  *  IS  16  n  18  19  ffl  21  ZL  Z3  24  Z526  Zl  X  23  3031  3233  34353637  3839  4041 
WEIGHT,  IN  HEKTOGRAMS 

Fio.  5. — Polygons  showing  variation  in  weight  of  pure  Polish  (P) 
and  pure  Flemish  (F)  rabbits,  and  of  their  FI  and  F2 
hybrid  offspring. 

Figure  5  shows  the  effect  upon  weight  of  the  widest  of  the  three 
crosses,  that  between  Polish  and  Flemish.  The  parental  groups 
are  separated  by  over  twenty  classes.  F!  lies  midway  between  them, 
its  mean  falling  in  class  25.  The  variation  polygon  is  rather  flat 
and  wide,  which  would  seem  to  indicate  lack  of  complete  genetic 

uniformity  in  one  or  both  parent  races. 
FI  is  of  similar  form,  but  is  shifted  about 
four  classes  farther  to  the  left.  A  sim- 
ilar movement  of  the  mean  occurred  in 
the  Polish-Himalayan  cross  between  the 
FI  and  the  F2  genera- 

-  tions.  The  variability,  as 

J^jn^r  measured  by  the  stand- 

_ c£        Mm      _ ard    deviation,    has    in- 
creased by  about  25  per 
cent,  from  198  grams  in 
to  257  grams  in  F2. 


WEIGHT,  IN  HEKTOGRAMS 


Fio.  6. — Polygons  showing  variation  in  weight  of  pure 
Himalayan  (If)  and  pure  Flemish  (F)  rabbits, 
and  of  their  F,  and  F,  hybrid  offspring. 


Figure  6  shows  for 
the  Himalayan-Flemish 
cross  the  variability  in 

weight  of  F!  and  F,.  F!  is  strictly  intermediate  between  the 
parental  races.  Its  mode  lies  in  class  27,  but  the  average  is  somewhat 
higher,  being  2,827  grams  (table  3).  The  mode  of  F,  lies  three  classes 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  13 

lower  in  class  24,  the  mean  being  2,472  or  about  three  and  a  half 
classes  lower  than  FI.  The  variability  of  F2  is  about  40  per  cent 
greater  than  that  of  Fi,  being  230  grams  instead  of  162. 

In  neither  of  the  Flemish  crosses  does  the  F2  variation  extend  up- 
ward into  the  range  of  pure  Flemish,  but  is  separated  from  it  by  from 
four  to  seven  vacant  classes.  In  other  words,  the  larger  parental 
type  is  not  recovered  in  F2,  doubtless  because  the  number  of  inde- 
pendent genetic  factors  involved  is  too  great.  If  the  larger  parental 
type  is  not  recovered,  it  is  not  to  be  expected  that  the  smaller  type 
would  be  recovered,  since  this  would  involve  a  chance  recombination 
of  factors  equally  improbable  of  realization  in  a  limited  number  of 
offspring;  but  in  reality  the  F2  range  does  in  every  case  extend  down- 
ward into  the  range  of  the  smaller  parent  type;  therefore  either  the 
smaller  type  is  more  readily  recovered,  or  what  appears  to  be  the 
smaller  type  recovered  in  F2  is  really  not  such,  but  is  a  new  genetic 
combination  or  combinations  which  resemble  in  gross  weight  the 
original  parental  type.  The  latter  alternative  seems  more  probable. 
This  view  is  supported  by  the  observations  on  ear-length,  which 
character  is  closely  correlated  with  weight,  and  yet  in  regard  to 
which  neither  the  small. nor  the  large  parental  type  is  recovered  in 
F2,  all  F2  variates  occurring  in  the  intermediate  region. 

EAR-LENGTH. 

Ear-length  is  a  character  easier  to  study  than  body-weight,  because 
the  adult  condition  is  attained  earlier  and  the  races  studied  are  more 
sharply  distinguished  as  to  ear-length  than  as  to  weight.  The  ears, 
as  a  rule,  have  attained  their  full  growth  at  the  age  150  days,  or  even 
earlier  in  the  case  of  the  Polish  race,  whereas  the  weight  continues 
to  increase  slowly  after  that  age. 

The  ear-length  was  recorded  at  the  same  time  that  the  rabbits 
were  weighed,  though  less  frequently,  as  little  change  was  noted  in 
the  ear-length  after  the  age  150  days.  After  a  rabbit  had  attained 
that  age  his  ears  were  measured  merely  often  enough  to  make  sure 
that  no  further  change  had  occurred  and  that  the  earlier  measure- 
ments had  been  accurate.  A  variation  of  1  or  2  millimeters  was 
frequently  noted  in  the  measurements,  and  the  final  rating  of  each 
rabbit  was  accordingly  based  on  the  approximate  mean  of  the 
recorded  measurements.  The  measurement  taken  was  read  from  a 
ruler  placed  between  the  base  of  the  right  ear  and  the  head,  the  ear 
being  then  held  vertically  against  the  ruler  and  slightly  stretched 
and  the  reading  made  at  the  ear-tip.  Small  races  of  rabbits  have 
short  ears;  large  races  have  both  longer  ears  and  longer  skulls,  as  we 
shall  see. 

The  variation  in  ear-length  of  the  groups  of  rabbits  studied  is 
shown  graphically  in  figure  7.  The  Polish  rabbits  studied  range 


14 


GENETIC   STUDIES   OF   RABBITS   AND    RATS. 


in  ear-length  from  81  to  88  millimeters,  Himalayan  from  92  to  97 
millimeters  or  about  1  centimeter  longer-eared  than  Polish,  while 
the  three  Flemish  individuals  used  as  parents,  notwithstanding  their 
diversities  in  weight,  are  remarkably  uniform  in  ear-length,  ranging 
from  143  to  147  millimeters,  or  about  6  centimeters  greater  than 
Polish  and  5  centimeters  greater  than  Himalayan.  The  three  races 
are  very  distinct  and  each  by  itself  very  uniform. 

The  data  on  the  ear-length  of  the  cross-bred  rabbits  is  summarized 
in  table  4  and  is  shown  graphically  in  figure  7. 


CAR   LENGTH,  IN  CENTIMETERS 

Fio.  7. — Polygons  showing  variation  in  ear-length  of  the  three  pure  races  of  rabbits  and  of  their 
Fi  and  Fj  hybrid  offspring. 

In  the  cross  between  the  Polish  and  Himalayan  breeds,  which 
differ  in  ear-length  by  about  10  millimeters,  long  ear  appears  to  be 
completely  dominant.  Variation  is  about  the  mode  of  the  Himalayan 
race  and  the  average  is  practically  the  same  (94.8  in  the  Himalayan, 
94.9  in  the  FI  group).  But  in  F,  the  variation  is  much  greater  and 
the  range  extends  downward  so  as  to  include  the  mode  of  the  Polish 
race  as  well  as  upward  to  cover  the  entire  range  of  the  Himalayan 
race  and  of  FI. 

The  cross  of  Himalayan  with  Flemish  gives  results  which  are  easier 
to  interpret.  These  two  races  considered  singly  are  very  uniform  in 
ear-length.  Each  varies  closely  about  a  mode  widely  separated 
from  that  of  the  other  race  (see  fig.  7).  F!  is  about  4  or  5  millimeters 
below  the  intermediate  and  varies  little.  F2  has  the  same  relation 
to  the  intermediate,  with  practically  the  same  mean,  but  is  much 
more  variable,  the  standard  deviation  (table  4)  having  risen  from 

)8  millimeters  in  F,  to  5.85  millimeters  in  F2,  and  the  range  from  8 
millimeters  to  24  millimeters.  Nevertheless,  the  range  of  F2  does  not 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  15 

extend  into  the  range  of  either  parental  race.  A  gap  of  8  millimeters 
separates  the  shortest-eared  F2  from  the  longest-eared  Himalayan 
rabbit,  and  a  gap  of  13  millimeters  separates  the  longest-eared  F2  from 
the  shortest-eared  Flemish.  Hence  it  is  clear  that  neither  parental 
combination  is  recovered  in  the  total  of  70  F2  individuals  studied. 
Clearly,  many  independent  factors  must  differentiate  the  parent  races 
as  regards  ear-length. 

The  cross  of  Polish  with  Flemish  is  a  still  wider  one  than  that 
just  described  and  Fi  is  somewhat  less  uniform.  It  is,  indeed,  about 
as  variable  as  the  F2  obtained  from  the  Himalayan-Flemish  cross, 
which  fact  indicates  a  greater  genetic  variability  in  the  Polish  than 
in  the  Himalayan  race  as  regards  ear-length.  Again,  in  this  cross 
FI  falls  below  the  intermediate  between  the  means  of  the  parent 
races  by  about  5  millimeters.  F2  shows  greatly  increased  variability 
as  compared  with  FI.  The  range  has  risen  from  14  to  30  millimeters, 
and  the  standard  deviation  from  3.76  to  6.05  millimeters  (see  table  4). 
Nevertheless,  the  range  of  F2  does  not  extend  into  that  of  either 
parental  race.  Four  vacant  classes  separate  it  from  the  range  of 
pure  Polish  and  20  vacant  classes  separate  it  from  the  range  of  pure 
Flemish.  It  accordingly  approaches  the  smaller  race  more  nearly 
than  the  large  one  (as  in  weight),  but  neither  parental  condition 
reappears  in  F2,  although  this  consists  of  131  individuals.  Again  we 
are  forced  to  conclude  that .  numerous  independent  genetic  factors 
affecting  ear-length  differentiate  the  parent  races. 

The  question  may  be  raised  whether  there  is  a  difference  between 
the  sexes  as  regards  ear-length,  as  there  appears  to  be  in  regard  to 
weight.  Table  5  answers  this  question  in  the  negative.  The  sexes 
differ  very  little  in  ear-length  and  neither  is  consistently  greater  than 
the  other  throughout  the  groups. 

BONE  MEASUREMENTS. 

The  length  of  the  skull  has  been  measured,  in  these  studies,  from 
the  notch  in  the  ventral  margin  of  the  occipital  foramen  to  the 
anterior  surface  of  the  incisor  teeth  in  a  straight  line,  measurement 
being  made  with  a  caliper  rule  and  readings  taken  in  tenths  of  milli- 
meters. Differences  in  skull-length  between  the  races  of  rabbits 
studied  are  less  in  amount  than  those  which  distinguish  these  same 
races  as  regards  ear-length.  But  it  is  desirable  to  ascertain  whether 
skull-length  differences  are  inherited  in  a  similar  way  and  whether 
they  are  correlated  with  differences  in  ear-length  and  body-weight. 
Hence  the  study  of  skull-length  will  have  value,  even  though  its 
results  are  not  as  clear-cut  as  those  derived  from  other  studies. 

Polish  rabbits  have  a  skull-length  of  from  63  to  69  millimeters. 
Himalayan  rabbits  have  somewhat  longer  skulls,  ranging  from  66 


16  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

to  72.5  millimeters.  The  skull-lengths  of  5  Flemish  rabbits  studied 
range  from  82.5  to  88  millimeters  (see  table  6). 

The  cross  between  Polish  and  Himalayan  rabbits  produced  off- 
spring surpassing  both  parent  races  in  skull-length,  as  in  body- weight, 
a  manifestation,  no  doubt,  of  heterosis  or  cross-bred  vigor.  The 
FI  averaged  70.2  millimeters  in  skull-length,  the  larger  parent  race 
averaging  68.9  millimeters,  the  intermediate  between  the  parents 
being  67.3  millimeters.  The  average  skull-length  of  F2  in  this  cross 
was  exactly  equal  to  that  of  the  larger  parent.  It  would  seem  that 
the  pure  Polish  and  Himalayan  races  may  have  been  below  their 
genetic  possibilities  in  skull-length,  owing  perhaps  to  inbreeding. 

The  Himalayan-Flemish  cross  (table  6,  F,,  H.XF.)  produced  Ft 
animals  averaging  a  little  larger  than  the  intermediate  between  the 
parent  races,  and  Ft  animals  averaging  a  little  less.  But  the  F2 
animals  were  more  variable  than  the  F!  animals,  their  standard 
deviation  in  skull-length  being  2.85  millimeters  as  compared  with 
1.79  millimeters  for  FI.  The  Polish-Flemish  cross  produced  an  Fj 
generation  close  to  the  intermediate  between  the  parent  races  as 
regards  skull-length,  but  FI  fell  more  than  2  millimeters  below  the 
intermediate.  Again  Fj  was  more  variable  than  FI,  the  standard 
deviations  being  3.15  and  1.18  respectively. 

Tables  7  and  8  show  the  variation  of  the  several  groups  of  rabbits 
in  skull-width  measurements  taken  anteriorly  and  posteriorly  respec- 
tively to  the  orbit.  It  appears  that  Polish  rabbits,  though  weighing 
less  than  Himalayan  rabbits  and  having  shorter  skulls,  nevertheless 
have  skulls  slightly  broader.  The  F!  rabbits  from  the  Polish-Hima- 
layan cross  have  skulls  broader  than  those  of  either  parent  (as  well 
as  longer,  see  table  6),  and  this  superiority  is  retained  in  part  in  the 
FI  generation.  These  statements  apply  both  to  the  anterior  and 
to  the  posterior  skull-width  measurements.  Although  the  Polish 
rabbits  have  slightly  broader  skulls  than  the  Himalayans,  neverthe- 
less they  do  not  transmit  as  much  skull-width  in  crosses  with  Flemish 
as  do  the  Himalayans,  for  in  every  case  the  skull-width  of  the  Hima- 
layan-Flemish cross-breds  is  slightly  greater  than  that  of  the 
Polish-Flemish  cross-breds.  The  explanation  probably  is  that  the 
Himalayans  transmit  greater  general  body-size  (weight)  in  crosses 
with  Flemish  than  the  Polish  do.  Skull-width  is  sufficiently  involved 
in  the  general  increase  of  all  bodily  dimensions  to  more  than  offset 
the  specific  tendency  of  Polish  to  transmit  a  broad  skull;  for  in 
skull-length  (table  6),  the  Himalayan-Flemish  cross-breds  exceed 
the  Polish-Flemish  cross-breds  even  more  than  in  skull-width. 

The  amount  of  variability  in  skull-width,  as  indicated  by  the 
standard  deviation  (tables  7  and  8),  is  too  erratic  to  have  any  par- 
ticular significance.  F,  is  not  uniformly  more  variable  than  F!  in 
these  cases. 


GENETIC   STUDIES  OF  RABBITS  AND   RATS.  17 

In  studying  bone-measurements,  the  length  of  3  leg-bones  has  been 
investigated,  that  of  the  tibia,  the  femur,  and  the  humerus  (tables  9 
to  11).  The  bones  measured  are  from  the  right  side  of  the  body. 
The  results  are  very  similar  in  all  three  cases.  The  Polish-Himalayan 
cross  is  followed  by  such  increase  in  vigor  that  the  cross-breds  of 
both  the  F!  and  the  F2  generations  surpass  in  bone-dimensions  the 
intermediate  between  the  parent  breeds,  but  the  Flemish  crosses 
produce  offspring  which  even  in  FI  fall  slightly  below  the  interme- 
diate between  the  parent  breeds,  and  in  F2  fall  below  it  still  more. 
In  every  case  F2  is  more  variable  than  FI. 

CORRELATION. 

The  question  may  properly  be  raised  whether  the  same  genetic 
factors  affecting  size  operate  in  all  parts  of  the  body,  or  whether 
there  are  special  factors  affecting  the  size  of  each  part.  The  latter 
view  is  favored  by  Davenport  in  his  studies  of  human  stature;  the 
former  seemed  to  me  to  be  indicated  in  the  statistics  of  rabbit  meas- 
urements published  by  MacDowell  (1914).  Wright  (1918),  from  a 
statistical  analysis  of  the  same  data,  concludes  that  both  general  and 
special  factors  are  indicated.  The  present  investigation  should  be 
able  to  throw  further  light  on  the  subject.  If  two  parts  or  dimen- 
sions of  the  body  are  influenced  by  the  same  genetic  agencies,  they 
should  vary  in  unison,  as  the  genetic  agencies  are  made  to  vary  by 
means  of  cross-breeding.  If  they  are  influenced  by  different  genetic 
agencies,  they  should  vary  independently  of  each  other.  For  this 
reason  it  is  desirable  to  study  the  correlation  existing  between  each 
pair  of  size-characters  studied. 

The  results  of  such  a  study  are  contained  in  the  correlation  tables 
(tables  12  to  29).  These  show  strong  correlation  in  every  case 
between  size  of  the  body  as  a  whole  and  size  of  each  of  its  parts,  as 
well  as  between  different  parts  of  the  body.  Most  of  the  correlation 
coefficients  (table  30)  lie  between  0.80  and  0.90,  where  1.00  would 
indicate  complete  identity  of  all  agencies  affecting  size,  whether 
genetic  or  non-genetic.  The  highest  correlations  are  found  in  com- 
paring the  lengths  of  the  long  bones  of  the  legs,  humerus  with  femur 
(0.906)  and  with  tibia  (0.904),  and  femur  with  tibia  (0.927).  Next 
in  closeness  of  correlation  comes  the  relation  between  skull-length 
and  the  length  of  the  leg-bones  (0.806  to  0.871),  but  the  correlations 
of  weight  with  bone-measurements  are  almost  as  close  (0.820  to 
0.852),  except  in  the  case  of  the  tibia,  where  the  coefficient  falls  to 
0.758.  There  is  a  very  similar  range  in  the  correlation  coefficients 
between  ear-lengths  and  weight  (0.836)  and  ear-length  and  the 
various  bone-measurements  (0.823  to  0.836),  except  again  in  relation 
to  the  femur,  where  occurs  the  lowest  correlation  of  the  entire  15 
studied,  viz,  0.741. 


18  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

In  the  case  of  MacDowelTs  observations  (Castle,  1914),  correlation 
coefficients  were  obtained  somewhat  lower  than  those  here  recorded, 
but  still  notably  high.  The  leg-bone  correlation  coefficients  (the 
highest  of  any  in  both  sets  of  observations)  were  in  MacDowell's 
rabbits  0.858,  0.857,  and  0.791,  where  the  present  observations  give 
0.927,  0.906,  and  0.904.  The  skull-length  correlation  with  tibia 
was,  in  the  former  case,  0.701,  in  the  latter  0.806.  In  general,  the 
correlations  run  about  10  per  cent  higher  in  the  present  set  of  obser- 
vations, which  is  probably  due  to  the  greater  range  of  variation  in 
size  in  the  lot  of  rabbits  OP  which  these  observations  have  been  made. 
The  number  of  rabbits  studied  in  the  two  cases  is  comparable,  a 
maximum  of  376  in  the  case  of  MacDowell's  rabbits,  of  348  in  the 
present  case.  But  the  range  of  size-differences  is  greater  in  the 
present  case.  For  example,  the  tibia  classes  in  MacDowell's  rabbits 
range  from  88  to  110  millimeters;  the  range  in  the  present  lot  is  from 
80  to  112  millimeters.  The  correlation  is  strongest  where  the  range 
is  most  extended,  for  at  the  ends  of  the  range,  where  only  individuals 
of  pure  race  occur,  genetic  differences  are  greatest  and  non-genetic 
agencies  sirk  into  insignificance,  whereas  at  the  middle  of  the  range 
Don-genetic  agencies  exert  a  relatively  greater  influence. 

That  this  is  so  can  be  shown  by  a  fuller  analysis  of  one  of  the 
correlation  tables.  Let  us  take,  for  example,  the  correlation  between 
femur  and  humerus  (table  24).  The  correlation  coefficient  (r)  for 
all  the  rabbits  (343)  taken  collectively  is  0.906.  For  the  pure  races 
only  (table  25)  it  is  0.980,  almost  perfect  correlation,  indicating  nothing 
but  genetic  agencies  at  work.  For  the  Fj  cross-breds  (table  26), 
which  should  be  no  more  variable  than  the  more  variable  of  the 
parent  races,  r  is  0.888,  much  lower  than  for  the  pure  races,  because 
now  only  intermediate  forms  are  present,  the  extremes  represented 
by  the  pure  parent  races  not  being  present.  For  F2  by  itself  (table 
27),  r  is  0.878,  very  nearly  the  same  as  for  Fi,  it  will  be  observed, 
although  the  genetic  diversity  is  greater.  For  F2  is  more  variable 
than  F!  as  regards  both  femur  and  humerus,  yet  the  correlation  indi- 
cated is  practically  the  same,  the  difference  being  no  greater  than  the 
probable  error.  If  there  were  independent  inheritance  of  factors 
affecting  the  size  of  femur  and  of  humerus  respectively,  the  correla- 
tion should  be  less  close  in  Fa  than  in  FI  because  of  recombination  of 
independent  genetic  factors,  but  such  is  not  the  case.  Hence  we 
are  forced  to  conclude  that  exactly  the  same  genetic  agencies  affect 
the  size  of  femur  and  humerus.  Similar  reasoning  would  lead  to 
the  conclusion  that  the  same  is  true  of  all  size  features  studied,  in- 
cluding not  only  bone-dimensions,  but  also  weight  and  ear-length. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  19 

GENERAL  OR  LOCAL  SIZE  FACTORS. 

In  the  light  of  these  facts,  what  should  be  our  attitude  toward  the 
view  (expressed  by  some  students  of  human  heredity)  that  mixed 
races  are  likely  to  contain  individuals  with  physical  maladjustments 
and  disharmonies?  On  this  view  it  is  assumed  that  there  are  inde- 
pendent genetic  determiners  affecting  the  size  of  the  different  parts 
of  the  body.  If  so,  when  races  of  different  size  are  crossed,  recom- 
bination of  genetic  factors  will  in  later  generations  produce  some 
parts  larger,  others  smaller,  than  the  general  average  of  the  races 
crossed.  This  will  result  in  disharmonic  combinations,  as,  for 
example,  hearts  too  large  or  alimentary  tracts  too  short  for  the  bodies 
in  which  they  are  found.  Is  there  any  real  ground  for  such  appre- 
hension? I  think  not.  There  is  in  health  a  perfect  correlation  in 
size  of  each  part  with  every  other  part  of  the  same  body  and  with 
the  size  of  the  body  as  a  whole.  The  modern  sciences  of  embryology 
and  physiology  tell  us  why  this  is  so.  It  is  (1)  because  development 
of  the  individual  from  the  fertilized  egg  is  so  largely  epigenetic,  each 
stage  growing  out  of  its  immediate  predecessor;  and  (2)  because  it  is 
so  largely  controlled  by  internal  secretions. 

The  view  of  the  genetic  independence  in  size  of  the  various  parts 
of  the  body  is  a  sporadic  relapse  into  preformationism,  such  as  was 
perhaps  excusable  to  the  Grecian  mind  when,  without  the  control  of 
observational  or  experimental  science,  it  fancied  animals  to  arise  by 
chance  coming  together  of  arms,  legs,  and  other  parts  which  originally 
floated  free  and  unconnected  in  primordial  slime.  The  day  for  such 
preposterous  ideas  is  past.  There  may  be  valid  reasons  why  mixing 
of  the  more  distinct  human  races  should  not  be  advocated,  reasons 
perhaps  sociological,  but  there  need  be  no  fear  that  an  animal  or- 
ganism will  result  whose  parts  are  not  properly  coordinated.  We 
are  only  beginning  to  understand  the  mechanism  of  such  coordination, 
through  studies  of  the  ductless  glands,  but  it  is  already  clear  that 
such  coordination  and  control  are  very  complete  and  are  adequate 
for  the  production  of  harmonic  organisms  in  the  widest  racial  crossing 
possible  in  the  animal  kingdom. 

I  think  that  a  strong  probability  has  been  established  that  the 
genetic  factors  which  affect  size  in  mammals  are  general  in  their  action, 
exclusively  so.  In  this  last  particular  I  dissent  from  the  view  ex- 
pressed by  Wright  (1918)  who,  from  a  statistical  examination  of 
MacDowell's  data,  concluded  that  the  genetic  factors  indicated 
were  in  minor  part  special  and  local  in  action.  Davenport  has  advo- 
cated a  similar  view  concerning  the  inheritance  of  human  stature, 
but  on  grounds  which  appear  to  me  to  be  inadequate  for  two  reasons: 
first,  because  of  the  imperfect  character  of  his  data,  and  secondly 
because  of  unwarranted  deductions  from  them.  Measurements  of 
the  several  elements  of  human  stature  made  on  the  living  subject 


20  GENETIC  STUDIES   OF   RABBITS   AND   RATS. 

are  far  from  being  precise  and  consequently  correlations  between 
these  measurements  are  unreliable.  Yet  such  is  Davenport's  entire 
material.  He  resolves  the  total  stature  (standing  height)  into  four 
elements,  only  two  of  which  are  capable  of  direct  measurement,  viz, 
the  "fibula"  and  the  "torso."  The  first  element  of  the  total  stature 
is  the  "fibula,"  which  is  the  "height  of  fibula  head  (attachment  of 
external  lateral  ligament)  from  the  floor."  The  second  element, 
the  "femur,"  is  obtained  by  subtracting  from  the  standing  height, 
first  the  "fibula,"  and  then  the  "sitting  height."  The  third  element, 
the  "torso,"  is  obtained  by  a  measurement  from  chair-bottom  to 
upper  end  of  sternum,  and  is  likely  to  be  vitiated  (as  is  the  sitting- 
height)  by  amount  of  flesh  or  fat  or  clothing  on  buttocks.  The 
fourth  element,  the  "head  and  neck,"  is  arrived  at  by  subtracting 
"torso"  from  "sitting  height."  There  are  altogether  too  many 
chances  of  error  or  inaccuracy  in  these  measurements  to  make  them 
comparable  in  reliability  with  measurements  made  on  the  actual 
skeletal  elements  of  individuals. 

Davenport  argues  for  the  independent  inheritance  of  the  four 
elements  of  stature  on  the  ground  that  races  and  families  have 
characteristically  different  proportions  of  the  total  stature  formed 
by  each  of  its  elements.  In  support  of  this  view  he  figures  (from 
"Martin,  1914")  side  by  side  photographs  of  a  "Dinka  negro"  and  a 
"Chiriguan  Indian."  The  enlargement  of  these  pictures  is  arranged 
so  as  to  make  the  individuals  of  seemingly  the  same  total  height, 
whereby  their  difference  in  proportions  is  obvious.  The  limbs  of  the 
negro  are  seen  to  be  relatively  long,  those  of  the  Indian  relatively 
short.  If,  now,  each  is  a  fair  representative  of  his  race,  we  must 
conclude  that  Dinka  negroes  inherit  as  a  racial  character  limbs 
relatively  long,  while  Chiriguan  Indians  inherit  as  a  racial  character 
limbs  relatively  short.  But  a  comparison  of  the  pictures  shows  also 
that  the  Indian  stands  much  nearer  the  observer  than  the  negro, 
as  the  size  of  his  head,  eyes,  hands,  and  feet  and  the  diameter  of  leg 
and  arm  are  much  greater.  It  is  his  nearness  to  the  observer  that 
makes  him  appear  as  tall  as  the  negro  in  the  picture.  He  is  accord- 
ingly of  absolutely  short  stature,  whereas  the  negro  is  of  absolutely 
tall  stature.  The  absolutely  tall  individual  (and  race)  accordingly 
has  relatively  long  limbs,  the  absolutely  short  individual  (and  race) 
has  relatively  short  limbs.  Is  this  association  accidental?  If  not,  we 
may  be  dealing  here  with  one  racial  difference,  not  two. 

Tall  stature  and  relatively  long  limbs  may  be  due  to  one  and  the 
same  genetic  cause,  and  not  be  independently  inheritable.  Daven- 
port's own  paper  indicates  that  this  is  probably  true.  He  repro- 
duces another  figure  (fig.  8)  from  "Martin,  1914,"  in  which  it  is 
shown  by  diagrams  that  the  proportions  of  the  human  body  change 
in  the  lifetime  of  the  individual,  the  limbs  becoming  relatively  longer 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  21 

as  the  absolute  stature  increases.  There  is  the  same  difference  in 
proportions  between  boy  and  man  as  between  Chiriguan  Indian  and 
Dinka  negro.  The  inheritance  of  boy  and  man  is  the  same;  one  is  a 
further  development  of  the  other. 

May  it  not  be  that  tall  and  short  human  races  are  the  result  of 
interruptions  at  different  stages  of  the  general  growth  process?  If  so, 
races  or  families  with  " relatively  long  fibula"  will  be  such  simply 
because  they  are  tall  races  or  families,  and  both  the  tallness  and  the 
long  fibula  will  be  due  to  one  and  the  same  ontogenetic  cause,  long- 
continued  growth.  It  is  no  accident,  probably,  but  the  result  of  a 
common  genetic  and  ontogenetic  agency,  that  South  Italians  are 
(1)  short  of  stature,  (2)  short-limbed,  and  (3)  mature  (cease  to  grow) 
early,  whereas  Swedes  and  Scotch  are  (1)  tall,  (2)  long-limbed,  and 
(3)  mature  late.  There  is  a  similar  difference  between  the  Polish 
and  Flemish  breeds  of  rabbits.  We  have  evidence  of  the  most  posi- 
tive sort  that  a  single  genetic  agency  is  responsible  in  one  case  for 
(1)  small  size,  (2)  short  ears,  and  (3)  early  maturity,  and  in  the  other 
for  (1)  large  size,  (2)  long  ears,  and  (3)  late  maturity.  In  one  case 
we  have  initial  energy  of  growth  small  (as  evidenced  by  the  form  of 
growth-curve)  and  soon  spent;  in  the  other  case,  growth  energy  is 
strong  and  persistent.  This  single  difference  will  account  for  all  the 
closely  correlated  size-differences,  respectively,  of  the  small  and  of  the 
large  races  of  rabbits. 

What  is  the  nature  of  this  genetic  agency?  Is  it  a  gene,  or  an 
assemblage  of  linked  genes,  or  what  is  it?  I  do  not  think  that  we  can 
give  a  full  and  final  answer  to  these  questions  at  present,  but  we  can 
at  least  outline  certain  possibilities  and  exclude  others. 

First,  inheritance  of  large  or  small  size  in  rabbits  is  influenced 
equally  by  the  father  and  by  the  mother.  No  difference  can  be 
detected  between  the  results  of  reciprocal  matings  between  large- 
sized  and  small-sized  races.  This  indicates  that  sperm  no  less  than 
egg  is  the  vehicle  of  transmission  and  makes  it  probable  that  the 
chromosomes  are  concerned  in  the  transmission.  If  so,  the  agency 
may  properly  be  a  gene  or  genes. 

THE  NUMBER  OF  SIZE  GENES. 

It  is  clear  from  the  results  of  crosses  between  large-sized  and  small- 
sized  races  of  rabbits  that  more  than  one  gene  must  be  involved, 
since  there  is  no  reappearance  in  F2  of  the  grand-parental  size-classes. 
The  question  may  be  raised  how  many  genes,  supposing  all  to  be  of 
like  influence  on  size,  will  account  for  the  observed  F2  distribution. 
There  are  two  ways  in  which  one  might  attempt  a  statistical  solution 
of  this  question.  He  might  consider  how  frequently  the  grand- 
parental  conditions  (extremely  large  or  extremely  small)  reappear  in 
F2  and  make  this  a  basis  for  estimating  the  number  of  independent 


22  GENETIC   STUDIES   OF   RABBITS   AND    RATS. 

genetic  factors  involved.  Thus,  reappearance  of  the  extremely 
large  type  in  1  individual  in  4  would  indicate  one  genetic  factor;  its 
reappearance  once  in  16  individuals  would  indicate  two  factors,  and 
so  on;  but  in  the  present  case  the  extremely  large  type  has  not  reap- 
peared at  all  in  F,,  so  that  this  method  is  scarcely  applicable.  On 
the  multiple-factor  theory,  it  may  be  that  too  small  a  number  of  F2 
individuals  has  been  produced  to  make  the  reappearance  of  an  extreme 
type  probable;  but  the  form  of  the  variation  curve  for  F2  would  still 
be  available  as  an  index  of  the  number  of  factors  involved,  even  if 
this  curve  was  not  sufficiently  extended  to  include  the  grand  -parental 
classes.  With  this  idea  in  mind,  I  have  suggested  (Castle,  1921)  a 
comparison  of  the  standard  deviation  of  F2  with  the  standard 
deviation  of  Fi  as  a  basis  for  estimating  the  number  of  independent 
factors  involved  in  cases  of  so-called  blending  inheritance.  Dr. 
Sewall  Wright,  who  has  kindly  assisted  in  this  matter,  gives  the  fol- 
lowing formula  for  computing  the  number  (n)  of  independent  factors 
involved  : 


In  this  formula  D  is  the  difference  between  the  means  of  the 
parental  (pure)  races,  a\  is  the  standard  deviation  of  Fi,  and  <r2  is 
the  standard  deviation  of  F2. 

In  table  31  are  shown  the  results  obtained  by  applying  this  formula 
to  the  six  most  important  measurements  studied  in  the  case  of  each 
of  the  three  different  racial  crosses.  For  the  Polish-Himalayan 
cross,  in  which  the  parent  races  do  not  differ  greatly  in  size,  a  differ- 
ence of  from  one  to  three  genetic  factors  is  indicated  by  the  different 
measurements  studied,  the  average  being  two  factors.  For  the 
Himalayan-Flemish  cross  the  indicated  number  of  factorial  differences 
ranges  from  5  to  10,  average  8.2.  In  both  these  crosses  the  results 
are  fairly  consistent  throughout  the  different  measurements.  But 
this  is  not  the  case  in  the  Polish-Flemish  cross.  Here  the  bone- 
measurements  give  low  values  (between  5  and  6),  evidently  too  low, 
since  they  are  less  than  those  of  the  Himalayan-Flemish  cross,  in 
which  the  parent  races  differ  less.  But  the  weight  and  ear-length 
values  are  high,  about  double  the  values  given  by  the  Himalayan- 
Flemish  cross.  The  average  for  the  series  is  10.5,  which  is  a  value  of 
the  proper  magnitude  in  relation  to  the  values  given  by  the  other 
two  series,  since  the  number  of  factorial  differences  between  Polish 
and  Flemish,  one  would  suppose,  should  about  equal  the  sum  of  the 
differences  (1)  between  Polish  and  Himalayan  and  (2)  between 
Himalayan  and  Flemish,  because  Himalayan  stands  in  size  between 
the  other  two  races.  It  is  noteworthy  that  the  results  given  by 
weight  and  by  ear-length  respectively  are  in  each  cross  very  similar. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  23 

The  fact  is  appreciated  that  these  are  at  best  rough  estimates, 
since  (1)  it  is  improbable  that  all  genetic  factors  affecting  size  have 
individually  the  same  amount  of  influence,  and  (2)  it  is  improbable 
that  the  FI  generation  is  in  each  case  devoid  of  genetic  variability, 
both  of  which  assumptions  are  made  in  the  formula  employed. 
Nevertheless,  the  results  may  have  some  value  as  indicating  whether 
many  or  few  chromosomes  are  concerned  in  the  inheritance  of  size  in 
these  crosses,  if  we  adopt  the  chromosome  hypothesis.  Any  addi- 
tional test  which  we  can  apply  to  that  hypothesis  will  have  cumula- 
tive value. 

The  number  of  chromosomes  in  the  rabbit,  according  to  the  sum- 
mary of  Miss  Harvey  (1920),  is  estimated  by  the  most  recent  ob- 
servers at  10  to  12,  an  earlier  estimate  being  14  to  18.  It  would 
accordingly  seem  probable,  on  the  chromosome  hypothesis,  that  all 
the  chromosomes  are  concerned  in  size  inheritance  in  such  a  wide  cross 
as  that  between  Polish  and  Flemish  Giant  rabbits,  while  in  the  other 
crosses  part  only  of  the  chromosomes  are  concerned. 

We  should  by  this  method  not  expect  to  find  a  number  of  factors 
indicated  greater  than  the  total  number  of  chromosomes,  since  even 
if  several  or  many  genes  in  a  single  chromosome  influenced  size, 
these  would  not  appear  in  the  general  result  as  independent  agencies, 
but  as  a  single  agency  consisting  of  a  linked  system.  The  result  given 
by  this  formula  must  accordingly  be  interpreted,  not  as  indicating 
the  total  number  of  genes  affecting  size,  but  as  the  probable  number  of 
chromosomes  (or  linkage  systems)  containing  such  genes. 

SIZE  AND  SEX. 

The  relation  of  size  to  sex  in  rabbits  has  already  been  discussed 
briefly  in  connection  with  weight;  we  may  now  discuss  this  question 
further,  and  in  relation  to  bone-dimensions  and  ear-length  as  well 
as  weight.  For  this  purpose,  the  groups  of  cross-bred  rabbits  afford 
the  best  material,  because  their  numbers  are  largest  and  they  are 
free  from  possible  effects  on  size  of  different  degrees  of  inbreeding. 
The  pertinent  facts  are  brought  together  in  table  32.  It  will  be 
observed  that  males  are  consistently  larger  in  all  bone  measurements, 
but  females  surpass  in  weight.  Yet  none  of  the  differences  is  very 
great.  It  is  evident  that  the  male  is  a  bigger-framed  animal  than 
the  female  (as  in  mammals  generally),  though  the  female  puts  on 
more  flesh.  But  the  size-differences  of  the  sexes  are  less  than  in  most 
mammals.  In  length  of  leg-bones  the  male  exceeds  the  female  by 
percentages  ranging  from  0.5  to  1.5.  In  skull-length  the  difference 
is  very  slight,  0.1  or  0.2  per  cent.  But  in  males  the  skull-width, 
between  the  outer  edges  of  the  zygomatic  arches,  is  greater  by  2  or 
2.5  per  cent.  Wright  (1918),  on  the  basis  of  MacDowell's  observa- 
tions, assumed  that  sex  is  a  specific  differential  factor  affecting  the 


24  GENETIC   STUDIES   OF   RABBITS   AND    RATS. 

length  of  the  hind-leg  in  rabbits,  but  it  is  evident  from  table  32  that 
the  action  of  this  factor  is  general,  not  local,  and  that  it  affects  the 
general  framework  of  the  rabbit,  not  its  leg-length  alone  or  its  hind-leg 
rather  than  its  front-leg. 

In  the  size  of  the  soft  parts  of  the  body — as,  for  example,  ear- 
length  and  body-weight — females  in  general  surpass  males.  But  it  is 
possible  that  this  difference  would  not  hold  for  certain  small  races  of 
rabbits.  We  have  already  noted  that  in  our  pure  Polish  rabbits  the 
average  weight  of  the  males  was  actually  greater  than  that  of  females, 
although  in  all  the  large  races  and  in  all  our  cross-breds,  females  are 
heavier  than  males,  the  difference  amounting  to  about  5  per  cent. 
In  ear-length  there  is  very  little  if  any  difference  between  the  sexes. 
Males  have  slightly  longer  ears  among  the  Polish-Himalayan  cross- 
breds,  but  females  among  the  Flemish  cross-breds.  The  differences 
are  of  doubtful  statistical  significance. 

The  differences  in  size  due  to  sex  are  too  small  to  affect  materially 
the  correlation  coefficients  obtained  by  comparing  bone-measure- 
ments, ear-length,  and  weight,  as  in  tables  12  to  30.  Of  this  I  con- 
vinced myself  by  making  separate  correlation  tables  for  the  two 
sexes  in  the  case  of  weight  correlated  with  length  of  tibia,  in  which 
the  disturbance  due  to  sex  would  be  at  a  maximum,  since  males  and 
females  would  in  these  two  characters  diverge  most  and  in  opposite 
directions,  males  having  a  longer  tibia,  but  females  being  heavier. 
The  correlation  between  weight  and  tibia  based  on  both  sexes  is 
0.758±0.015  (table  20).  For  the  males  alone  it  is  0.745±0.023; 
for  the  females  alone  it  is  0.775 ±0.021.  The  correlation  is  not  in- 
creased by  tabulating  the  sexes  separately.  For  the  sexes  combined 
the  correlation  is  practically  the  mean  of  the  values  obtained  for  the 
sexes  separately.  Neither  sex  departs  more  than  the  probable  error 
from  the  combined  value. 

TESTS  FOR  LINKAGE  WITH   COLOR  OR  OTHER  COAT 
CHARACTERS. 

Hoshino  (1915)  demonstrated  the  existence  in  garden  peas  of  a 
strong  linkage  in  heredity  between  a  quantitatively  varying  char- 
acter, time  of  flowering,  and  red  color  of  the  flowers.  It  would  be  of 
interest  to  know  whether  in  animals  a  similar  linkage  exists  between 
large  or  small  size  and  any  particular  color  gene.  I  can  not  discover 
that  such  is  the  case  in  rabbits,  probably  for  the  reason  that  size  in 
rabbits  is  determined  by  genes  located  in  many  or  all  chromosomes, 
whereas  each  color  gene  is  located  in  a  single  chromosome.  In  each 
of  the  two  crosses  with  Flemish,  a  different  albino  allelomorph  was 
introduced  by  the  small-sized  parent.  Albinism  was  completely 
recessive  in  F,,  but  reappeared  in  Ft  in  approximately  one-fourth  of 
the  individuals.  If  any  linkage  existed  between  albinism  and  small 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  25 

size,  a  majority  of  the  F2  albinos  should  have  been  of  small  size, 
averaging  less  in  weight  than  their  colored  brothers  and  sisters. 
Such  was  not  the  case.  In  the  Polish-Flemish  cross,  29  out  of  113 
F2  individuals  reared  to  maturity  were  albinos.  The  average  adult 
weight  of  the  albinos  was  2,155  grams,  that  of  the  entire  F2  population 
was  2,128  grams.  The  albinos  were  actually  a  little  larger  than  the 
average,  although  they  inherited  their  albinism  from  the  small-sized 
grandparent.  Hence  no  linkage  is  indicated.  In  the  Himalayan- 
Flemish  cross  a  similar  result  was  obtained;  11  out  of  62  adult  Fs 
individuals  were  Himalayan  albinos.  They  averaged  in  weight  2,535 
grams,  the  average  for  the  entire  population  (62)  being  2,468  grams, 
or  slightly  less.  The  small  size  of  the  Himalayan  grandparent  did 
not  make  the  Himalayan  individuals  any  smaller  (or  even  quite  as 
small)  as  their  colored  brothers  and  sisters.  Hence  no  linkage  is 
indicated. 

Yellow  color  and  dilute  pigmentation  are  two  recessive  unit- 
characters  which  were  transmitted  by  the  Polish  male  used  in  the 
Polish-Flemish  crosses,  but  were  not  transmitted  by  the  Flemish 
animals  used  in  those  crosses.  This  fact  affords  an  opportunity  to 
test  the  occurrence  of  linkage  between  small  size  and  either  yellow 
or  dilute  pigmentation. 

Three  yellow  F2  males  averaged  in  adult  weight  2,133  grams. 
The  entire  group  of  28  F2  males,  of  which  the  3  yellows  formed  a  part,1 
all  having  descended  from  the  same  pair  of  grandparents,  averaged 
2,156  grams,  substantially  the  same  amount.  Hence  there  is  no 
indication  of  linkage  between  yellow  and  small  size. 

Fourteen  F2  dilute  individuals  derived  from  the  mating  just  men- 
tioned or  from  other  reciprocal  Polish-Flemish  matings  averaged  in 
weight  2,086  grams,  while  the  average  weight  of  the  entire  F2  gener- 
ation in  this  cross  was  2,126  grams,  which  is  only  40  grams  heavier. 
This  difference  again  is  too  small  to  give  any  probable  indication  of 
linkage  between  dilution  and  small  size. 

Another  recessive  coat-character,  angora  (long  woolly  hair), 
appeared  unexpectedly  in  the  F2  generation  of  a  cross  between  a 
Flemish  female  (7)  and  the  Polish  male  (3).  A  further  study  of  the 
case  showed  that  the  angora  character  was  transmitted  by  the 
Flemish  parent  but  not  by  the  Polish.  In  this  case,  then,  linkage, 
if  found  at  all,  should  be  found  between  large  size  and  angora  coat; 
10  adult  angoras  occurred  among  the  42  F2  young  reared  from  this 
mating.  The  angoras  averaged  in  weight  2,174  grams;  the  entire  Fs 
group  averaged  2,194  grams,  or  20  grams  heavier.  Clearly,  there- 
fore, angora  was  not  linked  with  large  size. 

1  The  reader  may  wonder  why  the  number  of  yellow  grandchildren  was  so  small.  In  reality  a 
fourth  yellow  individual  was  produced,  a  female,  but  she  died  before  attaining  adult  size. 
Further,  the  Polish  grandparent  transmitted  yellow  in  only  half  his  gametes,  so  that  only  part 
of  the  Fi  individuals  inherited  the  character  from  him. 


•_><;  GENETIC   STUDIES   OF   RABBITS   AND    RATS. 

It  can  therefore  be  stated  with  confidence  that  no  linkage  is  found 
between  large  or  small  size  and  the  four  coat-characters,  albinism, 
dilution,  yellow,  and  angora.  A  reason  for  this  has  already  been 
suggested,  that  each  of  the  coat-characters  is  determined  by  a  single 
recessive  gene  borne  probably  in  a  single  chromosome,  and  in  the 
case  of  each  of  the  four  characters  in  a  different  chromosome,  whereas 
size  depends  on  many  genes  borne  probably  in  many  different  chro- 
mosomes or  in  all  the  chromosomes. 

In  table  33  is  recorded  the  color  of  each  rabbit  studied,  but 
an  examination  of  these  records  reveals  nothing  essentially  new  as 
regards  color  inheritance.  It  does,  however,  serve  to  confirm  the 
discovery  made  by  Punnett  (1912)  of  a  peculiar  form  of  the  extension 
factor  (E)  which  he  observed  in  the  offspring  of  a  certain  Himalayan 
rabbit.  To  be  sure,  Punnett  did  not  call  it  a  peculiar  form  of  the 
extension  factor,  but  rather  a  darkener  (D)  inseparably  coupled  with 
the  extension  factor  (E),  so  that  the  supposed  couplet,  darkened 
extension  (DE  of  Punnett),  behaved  as  the  allelomorph  of  ordinary 
extension  (E)  and  of  yellow  (e).  A  series  of  3  allelomorphs  was  thus 
established  by  Punnett's  observations,  and  it  would  seem  desirable 
for  simplicity  so  to  designate  them.  I  have  elsewhere  employed 
the  symbol  E'  for  Punnett's  darkened  extension  (DE).  The  order  of 
dominance  of  the  3  allelomorphs  is  E'  (dark  extension),  E  (ordinary 
extension),  e  (restriction  or  yellow). 

Our  observations  on  the  Flemish  crosses  reveal  the  probable 
source  of  Punnett's  peculiar  darkened  extension  found  in  his  Himala- 
yan doe  7.  No  Himalayans  of  pure  race,  that  we  have  had,  possessed 
the  darkened  extension,  but  it  is  regularly  present  in  Flemish  Giant 
rabbits  of  the  varieties  steel  gray  and  black.  Doubtless  Punnett's 
Himalayan  doe  7  was  derived  from  a  Flemish  cross  made  with  the 
idea  of  intensifying  or  darkening  the  pigmented  markings  of  the 
Himalayan  (nose,  ears,  tail,  feet). 

All  our  pure  Flemish  rabbits  have  possessed  darkened  extension. 
The  black  doe,  B,  was  apparently  homozygous  for  this  factor.  She 
transmitted  it  to  two  young,  d"2473  and  9  2474,  which  she  had  by 
the  Polish  male  3,  whose  formula  was  Ee.  These  two  young  are 
recorded  as  black,  but  as  full-grown  adults  it  was  noted  that  each  of 
them  at  times  showed  slight  indications  of  ticking  on  the  neck  or 
front  legs,  and  among  their  offspring  were  typical  steel  grays  (e.  g., 
93108,  93111,  c?3420),  similar  in  appearance  to  97  (plate  1,  F). 
That  animal  was  heterozygous  for  dark  extension,  her  formula 
being  E'E.  Mated  with  the  Polish  buck  3,  she  had  a  litter  of  9 
young,  of  which  5  were  gray,  2  steel-gray,  and  2  black.  The  5  gray 
never  produced  any  steel-grays  when  mated  inter  se,  which  shows 
that  they  did  not  inherit  darkened  extension,  but  only  ordinary 
extension,  E.  But  the  steel-gray  and  the  black  young  produced 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  27 

steel-gray  offspring  in  various  matings,  and  this  shows  that  they  did 
inherit  darkened  extension,  Er,  from  their  mother.  Their  sire,  as 
we  have  stated,  did  not  transmit  Ef,  but  was  of  the  formula  Ee. 
The  steel-gray  Flemish  buck  2,  used  in  crosses  with  both  Polish  and 
Himalayan  does,  was  also  heterozygous  for  dark  extension,  his 
formula  being  E'E.  By  Himalayan  does  (EE)  he  had  8  steel-gray 
and  9  gray  offspring  (see  table  33,  VI).  By  Polish  does  (EE  or  Ee) 
he  had  10  steel-gray  and  6  gray  young  (table  33,  V).  Unlike  97, 
he  had  no  black  young.  He  was  homozygous  for  the  gray  or  agouti 
factor  (A)  whereas  97  was  probably  heterozygous  for  this  factor. 
Hence  the  two  black  young  of  9  7,  her  formula  being  E'EAa,  but 
that  of  6*2  being  E'EAA. 

These  results  confirm  the  conclusions  of  Punnett  and  show  that — 

(1)  Any  individual  which  is  homozygous  for  darkened  extension  is 
devoid  of  agouti  ticking,  whether  or  not  the  agouti  factor  is  present. 
Examples  are  found  in  black  Flemish  and  black  Siberian  rabbits. 
(2)  Any  individual  which  is  heterozygous  for  dark  extension  (E'E  or 
E'e)  will  ordinarily  be  steel  gray  in  color  ("agouti-black,"  Punnett) 
if  the  agouti  factor  is  present,  either  heterozygous  or  homozygous,  but 
such  individuals  are  often  black  (showing  no  trace  of  agouti  ticking) 
in  their  first  coat,  although  they  develop  the  ticking  in  later  pelages. 

However,  some  individuals  of  formula  E'EAa  may  show  little  or 
no  ticking  in  their  adult  pelages,  as,  for  example,  the  FI  9  2474  and 
her  brother  6"  2473,  which  produced  steel-gray  young  as  well  as 
black  ones  when  mated  with  each  other.  If  the  allelomorph  of  E 
present  in  a  heterozygous  individual  is  e  rather  than  E}  the  steel-gray 
is  usually  (perhaps  always)  clearly  visible  in  the  adult  coat.  Punnett 
speaks  of  individuals  of  this  sort  as  invariably  " black,"  but  his 
classifications  were  apparently  based  exclusively  on  the  juvenile  coat. 

In  the  F2  generation  of  the  Flemish-Polish  cross,  but  not  of  the 
Flemish-Himalayan  cross,  appeared  dilute  pigmented  individuals 
having  dark  extension.  These  I  have  called  ' '  steel-blue  "and"  blue. ' ' 
They  correspond  with  the  classes  steel  gray  and  black  of  the  intense- 
pigmented  series.  From  the  fact  that  no  dilutes  appeared  in  Fs 
from  the  Flemish-Himalayan  cross,  it  is  clear  that  dilution  was 
introduced  in  the  Polish  race,  but  not  in  either  of  the  other  races. 
Similar  reasoning  shows  that  the  color  yellow  (e)  also  was  not  present 
in  either  the  Flemish  or  the  Himalayan  individuals  employed 
in  the  crosses,  but  only  in  the  Polish  individuals;  for  yellow  F2 
individuals  appear  in  the  Polish-Flemish  cross,  but  not  in  the 
Himalayan-Flemish  cross.  Finally,  angora  coat  appears  in  F2  of 
the  Polish-Flemish  cross,  but  not  in  either  of  the  other  crosses. 
Even  in  the  Polish-Flemish  cross  angora  appears  only  in  the  F2  of  a 
single  mating,  that  between  Flemish  97  and  Polish  c?3.  But  c?3 
was  employed  also  in  the  Himalayan-Polish  crosses,  yet  no  angora 


1?S  GENETIC   STUDIES   OF   RABBITS   AND    RATS. 

individuals  appeared  in  those  crosses.  Therefore  c?3  can  not  have 
transmitted  angora  coat.  Accordingly,  Flemish  97  must  have 
done  so.  She  was  not  employed  in  the  Flemish-Himalayan  cross, 
otherwise  we  should  have  expected  to  see  angora  individuals  in  the 
F,  of  that  cross  also. 

SUMMARY. 

1.  Studies  have  been  made  of  the  weight,  ear-length,  and  several 
bone-dimensions  of  three  races  of  rabbits,  and  of  the  first  and  second 
generation  hybrids  between  these  races. 

2.  Two  of  the  races  (Polish  and  Himalayan)  are  of  small  size,  like 
the  wild  rabbit  of  Europe,  the  ancestral  species.     The  third  race 
(Flemish  Giant)  is  very  large,  a  racially  new  condition. 

3.  Crosses  between  the  pure  races  produce  in  general  individuals 
of  intermediate  size  both  in  FI  and  F2,  so  that  the  inheritance  is 
correctly  described  as  blending.     But  when  the  parent  races  do  not 
differ  greatly  in  size  (as,  for  example,  the  Polish  and  Himalayan  races), 
the  size  of  FI  individuals  may  be  increased  by  heterosis  beyond  what  it 
would  be  through  inheritance  alone,  so  that  the  size  of  the  larger  pure 
race  is  approximated  or  even  surpassed.     Nevertheless,  with  the 
disappearance  of  the  heterosis  effect  in  F2  the  average  size  of  the 
cross-breds  sinks  to  a  strictly  intermediate  position. 

4.  The  heterosis  effect  is  seen  in  the  FI  generation  produced  by 
crossing  a  large  with  a  small  race,  no  less  than  in  the  cross  between 
two  small  races,  but  when  the  difference  in  size  between  the  races 
crossed  is  large,  the  heterosis  effect  is  not  sufficient  to  obscure  the 
essentially  blending  or  intermediate  character  of  the  inheritance  in 
FI.     It  merely  produces  a  rise  in  the  FI  average  size  above  the  strictly 
intermediate  position,  which  F2  in  every  cross  closely  approaches. 

5.  The  variability  in  size  of  F2  is  regularly  greater  than  that  of  FI, 
which  in  accordance  with  the  multiple-factor  hypothesis  is  regarded 
as  indicating  the  occurrence  of  genetic  factors  affecting  size  in  several 
different  chromosomes  or  linkage  systems. 

6.  An  attempt  has  been  made  by  statistical  methods  to  estimate 
how  many  different  chromosomes  (or  linkage  systems)  are  concerned 
in  the  inheritance  of  the  size-differences  found  in  the  three  race 
crosses,  with  the  following  average  results:  for  the  Polish-Himalayan 
cross,  at  least  two  chromosomes;  for  the  Himalayan-Flemish  cross, 
about  eight  chromosomes;  for  the  Polish-Flemish  cross,  ten  or  more 
chromosomes.     As  the  total  number  of  chromosomes  in  the  rabbit  is 
estimated  at  10  to  12  pairs,  it  seems  probable  that  all  chromosomes 
are  concerned  in  size-inheritance. 

7.  A  study  has  been  made  of  the  correlation  between  weight,  ear- 
length,  and  the  several  bone-dimensions  studied,  with  a  view  to  dis- 
covering whether  the  same  genetic  agencies  influence  size  in  different 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


29 


parts  of  the  body,  or  whether  factors,  independent  one  of  another, 
govern  size  in  different  parts  of  the  body.  The  conclusion  is  reached 
that  the  genetic  agencies  affecting  size  in  rabbits  are  general  in  their 
action,  influencing  in  the  same  general  direction  all  parts  of  the  body. 
The  same  would  probably  be  found  true  for  man  and  other  mammals, 
perhaps  for  vertebrates  in  general,  but  not  for  plants  in  which  hor- 
mone action  is  less  in  evidence. 

8.  No  linkage  relation  has  been  found  to  exist  between  size  and 
any  simple   (unifactorial)   Mendelian  character,  such  as  albinism, 
yellow  coat-color,  dilution,  or  angora  coat.     This  result  is  in  har- 
mony with  the  view  that  unifactorial  characters  have  their  genes 
located  each  in  a  single  chromosome,  while  size  is  influenced  by  genes 
located  in  many  or  all  chromosomes. 

9.  In  rabbits,  size  differences  correlated  with  sex  are  very  slight. 
In  skeletal  dimensions  the  adult  male  averages  larger  by  1  or  2  per 
cent,  but  in  weight  females  surpass  males,  particularly  in  the  larger 
breeds  of  rabbits;  yet  the  differences  are  so  small  as  not  to  disturb 
appreciably  the  correlation  coefficients  based  on  data  in  which  both 
sexes  are  included.     In  ear-length  no  significant  difference  between 
the  sexes  can  be  detected. 

TABLES. 

TABLE  1. — Average  weight  in  grams  of  rabbits  of  the  several  groups  studied,  at  various  ages. 
Data  used  in  the  construction  of  figure  8. 


Group. 

No. 

Age  in  days. 

30 

308 

605 
363 
377 
350 

40 

414 
422 
870 
459 
478 
521 

60 

549 
574 
1172 
661 
683 
769 

90 

779 
824 
1800 
1002 
1210 
1227 

120 

973 
1049 
2260 
1307 
1641 
1802 

150 

1133 
1240 
2630 
1580 
1988 
2154 

180 

1244 
1423 
2820 
1752 
2166 
2386 

210 

240 

1297 
1659 

1898 
2388 
2680 

270 

1311 
1705 

1927 
2443 
2719 

300 

1328 
1753 

1952 
2466 
2752 

330 

1344 
1800 

1962 
2485 
2789 

360 

1359 
1806 
3240 
1971 
2507 
2826 

Polish  
Himalayan  
Flemish  
Fi,  PXH  
Fi.  PXF  

20 
5 
2 
25 
27 
16 

1284 
1536 
2940 
1854 
2283 
2553 

F,.  PXH  

TABLE  2. — Comparative  weights  in  grams  of  the  two  sexes  in  the  groups  of  rabbits  studied. 


Group. 

No.  of  males. 

Av.  wt.  males. 

No.  of  females. 

Av.  wt.  females. 

Difference. 

Polish  

10 

1424 

10 

1403 

-   21 

Himalayan. 

1 

1880 

5 

1870 

-    10 

F,,  PXH.. 

15 

1957 

10 

2005 

+  48 

F,,  PXH.. 

23 

1560 

27 

1704 

+  144 

Fi,  PXF... 

14 

2469 

13 

2545 

+  76 

F,,  PXF... 

61 

2080 

52 

2176 

+  96 

F,,  HXF.. 

8 

2694 

8 

2886 

+  192 

F,,  HXF.. 

30 

2401 

32 

2531 

+  130 

30  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

TABLE  3.— Clarification  at  to  weight  of  the  several  groups  of  rabbits  studied. 

(Claw  10  includes  weights  1.000  to  1,099  grams;  class  11  includes  weights  1,100  to  1,199, 
etc.     There  are  no  data  for  columns  11,  32,  33,  35  to  39,  and  they  are  therefore  omitted.] 


Group. 

10 

1'2 

13 

14 

15 

10 

1 
1 

a 

10 
2 

17 

IS 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

34 

40 

1 

Average  in 
grams. 

1 

OQ 

Polish  
Himalayan. 
Flemish 

(•> 
1 

3 
8 

1 

'«> 

3 

1 
7 

1 

1 

1 

20 
6 
3 
25 
50 
27 
112 
16 
62 

1404 
1866 
3646 
1973 
1652 
2512 
2126 
2827 
2472 

142 

218 
233 
198 
257 
162 
230 

2 

1 

•• 

1 

'2 

Fi.  PXH... 
Ft.  PXH... 
F,,  PXF... 
Ft  PXF 

1 

i 

7 
13 

4 

7 

9 

6 
4 

10 

i 

i 

1C 

i 

3 

18 
7 

2 

1 
] 

1 

1 
11 

4 

5 

12 

7 

5 

13 

15 

4 

4 

10 

5 
1 

2 

0 

3 

2 

F»  HXF 

5 
5 

2 

3 

3 
3 

2 

1 

Ft  HXF 

TABLE  4. — Statistics  of  variation  in  millimeters  of  ear-length  in  the  several  groups  of 
Pi,  Fi,  and  Ft  rabbits  studied. 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Intermediate 
between 
parent  races. 

Polish        

23 

81  to    88 

83  6 

Himalayan  

6 

92  to    97 

94  8 

Flemish  
Pi,  P  X  H 

3 
25 

143  to  147 
90  to    98 

145.3 
94  9 

1  74 

89  2 

Ft,  P  X  H 

65 

85  to    99 

92  0 

3  62 

89  2 

F,,  H  X  F  
Ft.H  X  F 

17 
70 

112  to  119 
106  to  129 

115.6 
115  7 

2.08 
5  85 

120.0 
120  0 

Fi,  P  X  F 

27 

103  to  116 

109  3 

3  76 

114  4 

Ft,  P  X  F 

131 

93  to  122 

107  0 

6  05 

114  4 

TABLE  5. — Comparative  average  ear-length  in 
millimeters  of  males  and  females  in  the 
groups  of  rabbits  studied. 


Cross. 

Males. 

Females. 

Pi.  P  X  H... 

95.4 

94.2 

Ft,  P  XH.... 

92.5 

91.6 

Pi,  H  X  F.  .  .  . 

114.5 

116.6 

F,,H  X  F.... 

115.7 

116.5 

F,.  P  X  F.... 

109.1 

107.7 

F,,  P  X  F.  ... 

106.9 

107.1 

GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


31 


TABLE  6. — Variation  of  skull-length  in  the  several  groups  of  rabbits  studied. 
[All  measurements  in  millimeters.] 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Intermediate 
between 
parent  races. 

Polish 

21 

63      to  69 

65  7 

g 

66      to  72  5 

68  9 

Flemish  

5 

82.5  to  88 

85.5 

•  •  » 

F,,  P  XH  

25 

62      to  74.  5 

70.2 

2.16 

67.3 

F«.  P  XH  

53 

65      to  75 

68.9 

2.25 

67.3 

FlfH  X  F  

16 

76      to  82.  5 

78.9 

1.79 

77.2 

Fi,  H  X  F  

64 

69.  5  to  83.  5 

76.5 

2.85 

77.2 

Pi,  P  X  F  

27 

73      to  79.  5 

75.5 

1.18 

75.8 

F,,  P  X  F  

125 

63.  5  to  80 

73.1 

3.15 

75.6 

TABLE  7. — Variation  in  millimeters  of  anterior  skull-width  in  the 
several  groups  of  rabbits  studied. 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Polish 

20 

36      to  41 

37  6 

.25 

Himalayan 

8 

35      to  39  5 

37  0 

07 

Flemish 

5 

43  5  to  47 

45  3 

F,,P  XH  
F,,  P  XH  
Fi.H  X  F  
F»,  H  X  F  
Fi,  P  X  F  
Fj,  P  X  F 

25 
53 
17 
64 
27 
125 

36.  5  to  41.  5 
35.  5  to  40.  5 
39.  5  to  46 
38.  5  to  45 
40      to  44 
37      to  45 

39.4 
38.2 
42.9 
41.6 
42.3 
40.8 

.15 
.35 
.40 
.36 
.72 
1.36 

TABLE  8. — Variation  in  millimeters  of  posterior  skull-width  in  the  several 
groups  of  rabbits  studied. 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Polish  
Himalayan 

20 
8 

36      to  40.  5 
37      to  40 

38.0 
37.9 

0.96 
1.09 

Flemish  
Flf  P  X  H 

5 
25 

44      to  47 
36  5  to  42  5 

45.4 
39.5 

1.12 
.33 

F2,  P  X  H  

52 

35.  5  to  40 

38.1 

.17 

F,,H  X  F  
Fi,  H  X  F  
F,,  P  X  F  
F,,  P  X  F  

17 
64 
27 
125 

40.  5  to  44.  5 
38      to  45 
39.  5  to  44 
37      to  44.  5 

1    43.2 
42.0 
42.2 
40.8 

.95 
.36 
.32 
.20 

32  GENETIC  STUDIES  OF  RABBITS  AND   RATS. 

TABLE  9.— Variation  in  millimeters  of  length  of  tibia  in  the  several  groups  of  rabbits  studied. 


Race. 

No. 

Bang*. 

Average. 

Standard 
deviation. 

Intermediate 
between 
parent  races. 

Polish 

21 

79  to  89 

83.9 

2.26 

Himalayan 

8 

92  to  96 

93.9 

1.41 

5 

105  to  116 

111.0 

Fj.  P  X  H  

25 

86  to  96 

W.8 

2.38 

88.9 

FI   P  X  H 

54 

80  to  96 

89.8 

3  39 

88  it 

Fi.  H  X  F  

17 

95  to  105 

99.0 

2.44 

102.4 

FI.  H  X  F  

60 

90  to  105 

97.3 

3.10 

102.4 

Fi.  P  X  F  

27 

92  to  100 

96.2 

2.27 

97.4 

Ff.  P  X  F  

127 

82  to  104 

93.4 

4.75 

97.4 

TABLE  10. — Variation  in  millimeters  of  length  of  femur  in  the  several  groups  of 
rabbits  studied. 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Intermediate 
between 
parent  races. 

Poliah  
Himalayan  .    . 

20 
8 

68  to  76 
77  to  82 

72.3 
79  5 

1.71 
1  83 

Flemish 

5 

94  to  102 

97  6 

Fi,  P  X  H 

25 

73  to  82 

78  2 

1  92 

75  9 

Ft,  P  X  H 

54 

68  to  80 

76  2 

2  49 

75  9 

Fj.  H  X  F 

17 

84  to  91 

87  2 

1  61 

88  5 

Fj.  H  X  F 

6G 

78  to  90 

84  7 

2  86 

88  5 

Fj,  P  X  F 

27 

80  to  86 

83  3 

1  67 

84  9 

F,,  P  X  F 

126 

71  to  88 

80  4 

3  83 

84  9 

TABLE  11. — Variation  in  millimeters  of  length  of  humerus  in  the  several  groups  of 
rabbits  studied. 


Race. 

No. 

Range. 

Average. 

Standard 
deviation. 

Intermciliatc 
between 
parent  races. 

Polish 

21 

54  5  to  60  5 

57  7 

1  39 

Himalayan  

8 

61  5  to  63  5 

63  0 

0  75 

Flemish.  . 

4 

73      to  71  5 

75  0 

1..  P  X  H  
I».  P  X  H  

25 
51 

59      to  65 

•VI  ."i  to  64  5 

62.8 
60  9 

1  51 
2  37 

60.3 
60  3 

FI.  H  X  F 

17 

66      to  71 

68  8 

F».  H  X  F  
F,.  P  X  F  
Ft.  P  X  F. 

f.6 
27 
126 

62.  5  to  71.  5 
63.  5  to  68.  5 
56      to  70  6 

67.3 
66  2 

no    o 

2.26 
1.20 

69.0 
66.3 

GENETIC   STUDIES   OF   RABBITS   AND   RATS.  33 

TABLE  12. — Correlation  of  ear-length  with  weight. 


££  *• 

«•*  £ 

£J3  ?. 

*.s  a 

Ear-length  in  millimeters. 

1 

80 

83 

80 

89 

92 

95 

98 

101 

104 

107 

110 

113 

110 

119 

122 

125 

128 

131 

134 

137 

140 

143 

140 

10 

11 

12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 

Total  . 

2 
1 
3 

1 

3 
2 
3 
3 

1 

2 

3 
1 

i 

3 

1 

2 
3 
1 
1 
1 

1 

2 

4 
4 
4 
6 
3 
1 
1 
1 

1 
2 
1 

4 
4 
(j 
6 
3 
2 
2 
1 

1 

i 

4 
3 

2 
3 

i 

1 

G 
9 
12 
12 
16 
22 
23 
22 
24 
29 
18 
28 
31 
23 
15 
13 
8 
4 
3 

::: 

1 

4 
2 
5 
4 
1 
4 
6 

1 
1 

2 
2 
3 
3 

1 
1 

1 
1 

1 

1 
2 

4 
7 
5 
6 
6 
2 
3 

1 

i 

3 

7 

5 

8 
6 
2 
4 

1 
2 
6 
1 
3 
7 
5 
3 
3 

1 
1 

1 

"3 
3 
3 
2 
3 
2 
4 
2 
1 

1 

1 

2 
5 
4 

1 

1 
1 
1 

i 

1 

i 

i 

2 

2 

1 

i 

i 

1 
3-2-2 

~ 

1 

6 

13 

8 

14 

20 

r,i 

16 

29 

14 

38 

38 

33 

24 

16 

5 

3 

3 

2 

Mean  ear-length,  105.35±0.43.     S.  D.  ear-length,  3.86±0.10. 

Mean  weight,  2 14. 15 ±16.8.     S.  D.  weight,  448.6 ±11. 9.  r,  0.830 ±0.011. 

TABLE  13. — Correlation  of  ear-length  with  skull-length. 


Skull- 
length. 

80 

Ear-length  in  millimeters. 

I 

6 

16 
22 
43 
55 
45 
58 
U 
24 
10 
3 
2 

83 

86 

1 
3 

89 

1 

4 
4 
2 
1 

02 

95 

98 

101 

104 

107 

110 

na 

110 

119 

122 

125 

128 

», 

134 

137 

140 

143 

146 

62 
64 
66 
68 
70 
72 
74 
76 
78 
80 
82 
84 
86 

Total  . 

2 
2 

2 

1 

7 
2 
3 

5 

12 
7 
3 

1 

a 

8 
17 
2 
3 

1 

1 
7 
0 
1 

1 

4 
2 
3 

14 
6 

1 

1 
10 
4 
2 

3 
3 
8 
16 
9 
1 

5 
6 

12 
14 
2 
2 

3 

8 
12 
9 

1 

1 

8 
4 
5 
3 

9 

3 
7 
5 
2 

2 
1 

1 

1 
1 
1 

2 

1 

1 

1 
1 

3 

t 

~~ 

1 

6 

13 

X 

14 

27 

34 

17 

3(\ 

17 

40 

41 

82 

n 

17 

A 

3 

2 

«7 

Mean  ear-length,  105.45  ±0.42.     S.  D.  ear-length,  11. 46  ±0.28. 

Mean  skull-length,  73.03±0.16.     S.  D.  skull-length,  4.42±0.11.     r,  0.836±0.011. 


34 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 
TABUS  14.— Correlation  of  ear-length  with  humerus-length. 


H 

Ear-length. 

| 

SO 

1 

5 

83 

SO 

89 

1 

1 
4 

92 

95 

98 

101 

104 

107 

110 

113 

116 

119 

122 

125 

128 

131 

134 

i:57 

140 

143 

146 

64 

60 
68 
00 
02 
04 
00 
08 
70 
72 
74 
70 

Total. 

1 
4 
1 

2 

? 

1 

•; 

| 

2 
? 

i 

i 

4 
17 

23 
41 
78 
67 
58 
32 
16 
1 
1 
1 

j 

:: 

3 

3 

4 

3 

7 
14 

3 
21 

7 

4 

5 
3 

6 
13 
9 

6 
3 

7 
2 

4 
12 
10 
11 
2 
1 

1 

6 
19 
12 
3 

7 
14 
8 
7 

4 

9 
8 
2 

1 

8 
6 
3 

1 

3 

j 

3 

2 

1 

"l 

7 

13 

8 

13 

27 

34 

16 

30 

18 

41 

41 

36 

24 

17 

5 

3 

3 

1 

2 

339 

Mean  ear-length,  105.46  ±0.41.     S.  D.  ear-length,  11. 46  ±0.29. 

Mean  humenu,  64. 1 7  ±0. 13.    8.  D.  humerus,  3.73  ±0.09.    r,  0.823  ±0.01 1 . 

TABLE  15. — Correlation  of  ear-length  with  femur-length. 


?emur- 

length. 

Ear-length. 

1 

SO 

S3 

hO 

S9 

J2 

95 

98 

101 

104 

107 

110 

113 

11C 

119 

122 

125 

128 

131 

134 

137 

140 

143 

146 

08 
70 
72 
74 
70 
78 
80 
82 
84 
80 
88 
00 
02 
04 
00 
08 

Total 

2 
3 
2 

1 
1 
9 
1 
1 

1 

4 
6 
24 
23 
48 
48 
48 
55 
31 
30 
21 
2 

1 
343 

2 
5 

1 

3 
1 

7 

1 

6 
7 

10 
2 

2 
2 
9 
11 

7 
2 

3 
1 
8 
2 
1 
| 

1 
1 
| 
7 
I 
1 
2 

2 
4 
I 

6 
2 

2 
4 
11 

8 
9 
5 

4 

1 
3 
4 
10 
11 
7 
6 

4 
10 
6 
11 
4 
\ 

2 
7 

4 
4 
7 

6 
5 

4 
1 

i 
i 

2 
2 

2 
1 

1 
2 

i 
i 

1 

7 

1 

:w 

17 

30 

41 

2 

13 

8 

14 

28 

17 

43 

36 

24 

17 

6 

3 

3 

1 

Mean  ear-length,  106.46  ±0.41.     8.  D.  ear-length,  11.47  ±0.29. 
Mean  fcmur,  80.73±0.18.     8.  D.  femur,  6.00±0.12.     r,  0.828±0.011. 


GENETIC  STUDIES  OP  RABBITS  AND   RATS. 
TABLE  16. — Correlation  of  ear-length  with  tibia-length. 


35 


Tibia- 
length. 

Ear-length. 

1 

80 

83 

86 

89 

92 

95 

98 

101 

i 

3 
5 
4 
6 
5 
3 
3 

104 

107 

110 

113 

116 

119 

122 

125 

128 

131 

134 

137 

140 

143 

140 

80 
82 
84 
86 
88 
90 
92 
94 
96 
98 
100 
102 
104 
106 
108 
110 
112 

Total. 

3 

4 

1 
1 
7 
3 
1 

1 

1 

2 
4 

1 

5 
1 
4 
3 

1 

2 
3 
4 
8 
6 
4 

i 

i 
i 

2 
6 
10 

8 
5 

3 

4 
4 
3 
2 

5 
10 
13 
22 
29 
42 
65 
54 
41 
37 
23 
7 
4 

3 
1 
5 
3 

4 

i 

2 
3 
8 
10 
6 
5 
5 
2 
2 

1 

4 
3 

9 
7 
8 
9 

4 
8 
6 
7 
6 
3 
2 

1 
4 
5 
7 
7 

"5 
5 
2 
4 
1 

"3 
2 

i 

1 
2 

1 
1 

... 

1 

1 

1 

2 

7 

13 

8 

15 

27 

34 

17 

30 

17 

43 

41 

36 

24 

17 

6 

3 

3 

1 

1 

344 

Mean  ear-length,  105.42  ±0.41.     S.  D.  ear-length,  11. 48  ±0.29. 
Mean  tibia,  93.64  ±0.19.     S.  D.  tibia,  5.27  ±0.13.     r,.  0.741  ±0.016. 

TABLE  17.— Correlation  of  weight  with  skull-length. 


Skull- 
length. 

Weight  in  hektograms. 

Total. 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

34 

40 

62 
64 
66 
68 
70 
72 
74 
76 
78 
80 
82 
84 
86 

Total. 

? 

1 

1 

1 

2 

i 

5 
13 
20 
39 
51 
43 
56 
62 
23 
11 
2 
2 

1 

2 
1 

4 

2 
3 

2 
5 
2 
1 
1 

1 
4 
5 

2 

3 

4 

4 
2 

1 
1 

2 
7 
1 
2 
1 

2 

4 

1 

i 
i 

2 

i 
i 
i 

3 
9 
8 
2 

's 

8 

5 

1 

1 
5 
10 
4 

10 
6 
4 
3 

i 

6 
6 

12 
2 

3 

30 

... 

1 

5 
7 
5 

6 
8 
7 
1 
2 

2 

5 

7 
13 
4 
1 

2 
6 
7 
6 
2 

5 
4 
3 
1 

1 

5 

9 

12 

12 

16 

23 

22 

21 

24 

18 

26 

32 

23 

u 

13 

8 

4 

3 

2 

i 

318 

Mean  weight,  2,141.0±16.9.     S.  D.  weight,  447.0±11.9. 
Mean  skull-length,  73.17  ±0.16.     S.  D.  skull-length,  4.38±0.11. 


r,  0.852±0.010. 


36 


GENETIC  STUDIES  OF   RABBITS  AND   RATS. 
TABLE  18.— Correlation  of  weight  with  humerus. 


Hum*. 

Weight. 

Total. 

rua. 

10 

11 

1-2 

13 

14 

i:> 

If, 

17 

IN 

19 

M 

21 

n 

23 

24 

25 

26 

27 

28 

M 

•M 

34 

40 

64 
66 

68 
60 
62 
64 
66 
68 
70 
72 
74 
76 

Total. 

1 

o 

3 
16 
21 
39 
72 
59 
58 
31 
16 
1 
1 
1 

i 

3 
I 

1 

1 
•2 
•2 
1 

4 
4 
1 
3 

1 

'2 
•2 
1 

i 

5 
1 

4 

1 
6 

7 
8 
2 

1 
1 
7 
11 
I 

7 
9 
4 

4 
9 
1 

4 

2 
6 

14 
8 
1 

8 

7 
3 

6 
4 
11 
3 
2 

6 

7 
10 
4 
5 

6 
9 
0 
2 

2 

4 
6 
2 

2 
6 
6 
1 

1 
3 
3 
1 

2 

2 
1 

1 

1 

:;j 

28 

i 

I 

7 

13 

11 

I.', 

23 

•2-2 

I'D 

IB 

30 

18 

27 

n 

14 

13 

s 

4 

3 

•2 

1 

318 

Mean  weight,  2,146.5  ±16.8.     S.  D.  weight.  445.9. 

Mean  humerus,  64.26±0.14.     S.  D.  humerus,  3.75±0.10.     r,  0.820±0.012. 

TABLE  19.— Correlation  of  weight  with  femur. 


Femur. 

Weight. 

Total. 

10 

11 

13 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

34 

40 

68 
70 
72 
74 
76 
78 
80 
82 
84 
86 
88 
00 
02 
04 
06 
08 

Total. 

l 

1 

a 

2 
1 

1 

3 

•2 
•2 

i 

4 
2 
3 
1 

2 

3 
4 

•2 

1 

4 
3 
(i 
2 

4 
5 
21 
22 
45 
44 
43 
52 
28 
29 
20 
2 

3 
9 

Q 
4 
1 

3 
1 

9 
2 
2 

1 
2 
8 
7 
5 
1 
1 

6 
6 
6 
9 

4 
2 

6 
7 
8 

1 

3 
1 

6 
6 

8 
3 

2 

2 
2 
5 
10 
4 
5 
2 
j 

2 
6 
7 

4 
4 

2 

5 
1 

5 
3 

3 
5 
3 

2 
2 

3 

1 

i 

1 

1 
2 

4 

3 

1 
1 

14 

30 

1-2 

Hi 

18 

l 

(i 

8 

1-2 

23 

22 

19 

25 

27 

31 

M 

13 

8 

1 

i 

318 

Mean  weight,  2,143.0±16.9.     8.  D.  weight,  448.0±11.9. 

Mean  femur,  80.80±0.19.    S.  D.  femur,  5.03±0.13.    r,  0.841  ±0.011. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS.  37 

TABLE  20. — Correlation  of  weight  with  tibia. 


Tibia. 

Weight. 

Total. 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

34 

40 

80 
82 
84 
86 
88 
90 
92 
94 
96 
98 
100 
102 
104 
112 

Total  . 

i 

2 
1 
2 
1 

2 

1 
2 
1 

3 

4 
2 
2 

1 

2 

1 

1 
2 
1 
1 

1 
3 
1 
3 
4 
3 
1 

1 

5 
5 
4 
5 
4 
1 

i 
i 

2 

7 
7 
4 
4 
3 
? 

1 

3 
7 
6 
6 
1 

2 
3 

6 
1 
? 

i 

2 
2 
4 
4 

2 
3 
2 

4 
9 
12 

20 
27 
39 
61 
48 
38 
37 
22 
7 
4 
2 

2 
1 

2 
8 
3 

4 
3 

4 
2 
6 
4 
5 

2 
2 

7 
5 
2 
2 

2 
5 
3 
7 
3 
3 
1 

2 
4 
8 
2 
9 
4 
1 

1 
2 
6 
5 
1 
2 
1 

2 

1 

1 

1 

1 

1 
,1 

i 

6 

20 

25 

27 

32 

8 

4 

3 

i 

7 

13 

12 

16 

23 

22 

30 

18 

23 

14 

13 

2 

1 

320 

Mean  weight,  2,143.6±16.8.     S.  D.  weight,  446.6±11.9. 

Mean  tibia,  93.77  ±0.20.     S.  D.  tibia,  5.29  ±0.14.     r,  0.758  ±0.015. 


TABLE  21. — Correlation  of  humerus-length  with  skull-length. 


Humerus-length. 

Skull- 
length. 

Total. 

54 

56 

58 

60 

62 

64 

66 

68 

70 

72 

74 

76 

62 

2 

1 

5 

64 

1 

5 

5 

5 

16 

66 

4 

4 

7 

3 

7 

25 

68 

5 

I 

13 

14 

2 

42 

70 

14 

23 

14 

3 

54 

72 

5 

22 

11 

8 

1 

47 

74 

1 

2 

9 

23 

18 

3 

2 

58 

76 

3 

12 

21 

11 

5 

52 

78 

2 

6 

12 

4 

24 

80 

4 

4 

2 

10 

82 

1 

2 

1 

4 

84 

1 

1 

2 

86 

1 

1 

Total  . 

24 

78 

64 

60 

31 

1 

1 

5 

16 

42 

16 

2 

340 

Mean  humerus,  64. 16  ±0.13.     S.  D.  humerus,  3.77  ±0.09. 

Mean  skull,  72.96±0.16.     S.  D.  skull,  4.46±0.11.     r,  0.834 ±0.011. 


38  GENETIC   STUDIES   OF   RABBITS   AND    RATS. 

TABLE  22.— Correlation  of  femur-length  with  skull-length. 


Skull- 
length. 

Femur-length. 

Total. 

68 

70 

72 

74 

76 

78 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

100 

102 

62 
64 
66 

68 
70 
72 
74 
76 
78 
80 
82 
84 
86 
88 

Total. 

1 
1 
2 

1 

1 

4 

3 
9 
0 
7 

5 
16 
25 
43 
54 
47 
58 
53 
24 
10 
4 
2 
1 
1 

4 
4 
11 
2 

1 

1 

8 
12 
15 
10 
2 

i 

9 
16 
12 
6 
2 

4 
15 
9 
16 

4 
1 

6 

10 
18 
20 
1 

3 

9 
10 
6 
2 

1 
4 
14 
9 

i 

2 
I 

6 

7 
2 

1 

1 

1 
1 

i 

1 

1 

... 

4 

6 

25 

23 

48 

46 

49 

55 

30 

29 

21 

2 

2 

1 

1 

i 

343 

Mean  femur,  80.80  ±0.19.    8.  D.  femur,  5.20  ±0.13. 

Mean  skull,  73.06±0.16.     S.  D.  skull,  4.53±0.11.     r,  0.871  ±0.008. 

TABLE  VS.— Correlation  of  tibia-length  with  skull-length. 


Skull- 
length. 

Tibia-length. 

Total. 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

100 

102 

104 

106 

112 

116 

62 
64 
66 
68 
70 
72 
74 
76 
78 
80 

84 
86 
88 

Total. 

1 
1 
2 

2 
2 

4 
3 

1 

7 
4 
1 
1 

1 
3 
5 
5 
2 
5 

2 
2 
13 
2 
4 
3 
1 

.... 

2 
13 
13 
8 

4 
2 

'e 

4 
17 
13 
9 
5 
1 

5 
16 
25 
43 
54 
46 
58 
53 
24 
10 
14 
2 
1 

4 
13 
5 
18 
13 

5 
5 
10 
13 

7 
1 

1 
5 
7 
12 
7 
3 

i 

7 
4 
5 
5 

2 
4 
1 

1 

2 

1 

j 

. 

1 

4 

11 

14 

21 

27 

43 

55 

53 

41 

35 

23 

7 

4 

1 

2 

1 

342 

Mean  tibia,  93.74±0.20.     S.  D.  tibia,  5.45±0.14. 

Mean  •kulJ.  73.06±0.16.     8.  D.  skull,  4.54±0.11.     r,  0.806±0.015. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

TABLE  24. — Correlation  of  femur  with  humerus,  all  group*  included. 


39 


Hume- 

rus. 

Femur. 

Total. 

68 

70 

72 

74 

76 

78 

80 

82 

84 

86 

88. 

90 

92 

94 

96 

98 

54 
56 
58 
60 
62 
64 
66 
68 
70 
72 
74 
76 

Total  . 

3 
1 

1 
5 

4 
18 
24 
41 
79 
64 
61 
32 
16 
2 
1 

10 
13 
2 

2 
10 
11 

'is' 

28 
2 

V 

29 

8 

2 
7 
14 
6 

1 
11 

8 

1 

18 
26 

4 

4 
25 
26 

i 

23 

7 

1 

1 

2 

2 

25 

4 

7 

23 

48 

46 

49 

55 

31 

29 

20 

2 

2 

1 

343 

Mean  femur,  80.69  ±0.18.     S.  D.  femur,  5.08dh0.13. 

Mean  humerus,  64. 17  ±0.13.     S.  D.  humorus,  3.78  ±0.09.     r,  0.906  ±0.006. 

TABLE  25. — Correlation  of  femur  with  humerus,  pure  races  only. 


Hume- 
rus. 

Femur. 

Total. 

68 

70 

72 

74 

76 

78 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

54 
56 
58 
60 
62 
64 
66 
68 
70 
72 
74 
76 

Total  . 

1 
1 

1 
4 
1 

6 
4 

1 

2 
11 
6 
3 

7 

1 

•> 

2 

1 

3 

1 

2 

::i 

i 

2 
1 
1 

1 

2 

6 

11 

1 

4 

1 

3 

2 

1 

i 

33 

Mean  femur,  76.95.     S.  D.  femur,  8.06. 

Mean  humenis,  60.95.     S.  D.  humerus,  5.60.     r,  0.980  ±0.004. 


40 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 
TABLE  26.— Correlation  of  femur  with  humerus,  F,  only. 


Hume- 
rus. 

Femur. 

Total. 

72 

74 

76 

78 

80 

82 

84 

86 

88 

90 

58 
60 
62 
64 
66 
68 
70 

Total. 

1 

e' 

6 

1 
9 
1 

1 
4 
17 
14 
19 
11 
3 

2 

6 

1 
8 
2 

3 

5 

1 

3 
6 

4 
2 

1 

.... 

.... 

1 

2 

7 

11 

0 

12 

11 

9 

6 

1 

N 

Mean  femur,  82.64.     S.  D.  femur,  4.08. 

Mean  humerus,  65.58.     S.  D.  humeruB,  2.68.     r,  0.888  ±0.017. 

TABLE  27. — Correlation  of  femur  with  humerus,  Ft  only. 


Hume- 

rus. 

Femur. 

Total. 

68 

70 

72 

74 

76 

78 

80 

82 

84 

86 

88 

90 

64 
66 
68 
60 
62 
64 
66 
68 
70 

Total. 

2 

2 

7 
17 
34 
55 
50 
42 
21 
13 

4 
8 

2 
9 
9 

16 
20 
2 

8 
20 
6 

12 
21 
3 

3 

19 
20 

14 
6 

2 
4 
8 
6 

1 
7 
6 

1 

2 

1 

13 

20 

37 

34 

37 

42 

20 

20 

14 

1 

241 

Mean  femur,  80.67.     S.  D.  femur.  4.48. 

Mean  humenifl.  66.21.     S.  D.  humerus,  3.45.     r,  0.878  ±0.010. 

TABLE  28. — Correlation  of  tibia  with  humerus. 


Hume- 

I'ibia 

Total 

rus. 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

100 

102 

104 

1M 

112 

54... 

? 

3 

5 

56  

3 

7 

4 

2 

1 

17 

58  

1 

7 

12 

4 

24 

60  

3 

5 

14 

17 

3 

42 

62  

3 

7 

19 

29 

15 

4 

2 

79 

64  .  . 

2 

5 

19 

20 

13 

6 

65 

66  

4 

15 

21 

12 

g 

60 

68  

3 

3 

12 

10 

4 

32 

70  

4 

5 

3 

3 

16 

72  

j 

1 

2 

74  

1 

76  

1 

. 

Total. 

6 

11 

14 

22 

28 

41 

66 

53 

42 

36 

23 

7 

4 

1 

2 

344 

Mean  tibia,  93.64  ±0.19.     8.  D.  tibia.  5.35  ±0.13. 

Mean  humerus.  64.15±0.13.     S.  D.  humerus.  3.78 ±0  ()»      >,  0.904±0.006. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

TABLE  29.— Correlation  of  tibia  with  femur. 


41 


1 

Tibia. 

1 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

100 

102 

104 

106 

112 

116 

68... 
70... 

72 

2 
3 

1 
3 

7 

2 
11 

7 

3 
8 
25 
23 
49 
48 
49 
55 
31 
29 
21 
2 

74..  . 

1 

10 
5 

10 
12 
5 
1 

2 

18 
18 
5 

76... 
78... 
80... 
82... 
84... 
86 

14 

17 
18 
6 

6 
17 
25 
5 

2 
7 
18 
11 
2 
1 

..... 

6 
9 
17 
4 

6 

7 
10 

3 
3 
1 

2 
1 

88... 
90... 
92... 
94... 
96... 
98... 
102 

1 

1 

1 

2 
1 

1 
1 

1 
1 

1 

Total. 

5 

11 

14 

22 

28 

43 

56 

53 

41 

37 

23 

7 

4 

1 

2 

1 

348 

Mean  tibia,  93.69  ±0.19.     S.  D.  tibia,  5.48  ±0.14. 

Mean  femur,  80.76  ±0.18.     S.  D.  femur,  5. 19  ±0.12.     r,  0.927  ±0.005. 

TABLE  30. — Correlation  coefficients  derived  from  tables  12  to  £9. 


Table. 

Characters  correlated. 

Coefficient. 

Table. 

Characters  correlated. 

Coefficient. 

12 

Ear-length,  weight  .  .  . 

0.836±0.011 

22 

Femur,  skull-length.  . 

0.871  ±0.008 

13 

Ear-length,  skull 

23 

Tibia,  skull-length  .  .  . 

0.806  ±0.015 

length  

0.836±0.011 

24 

Femur,  humerus  

0.906  ±0.006 

14 

Ear-length,  humerus  . 

0.823  ±0.011 

25 

Femur,  humerus(pure 

15 

Ear-length,  femur.  .  .  . 

0.828  ±0.011 

races  only)  

0.980  ±0.004 

16 

Ear-length,  tibia  

0.741  ±0.016 

26 

Femur,  humerus  (Fi 

17 

Weight,  skull-length.  . 

0.852  ±0.010 

only)  

0.888  ±0.017 

18 

Weight,  humerus  .... 

0.820  ±0.012 

27 

Femur,  humerus  (Fi 

19 

Weight,  femur  

0.841±0.011 

28 

only)  

0.878  ±0.010 

20 

Weight,  tibia  

0.758  ±0.015 

28 

Tibia,  humerus  

0.904  ±0.006 

21 

Humerus,  skull-length 

0.834  ±0.011 

29 

Tibia,  femur  

0.927  ±0.005 

TABLE  31.— Number  of  size  factors  indicated  by  each  set  of  measurements  as  differentiating 
the  three  races  crossed. 


Race. 

Tibia. 

Femur. 

Humerus. 

Skull- 
length. 

Weight. 

Ear-length. 

Av. 

Polish-Himalayan  .  . 

2.1 

2.6 

1.0 

3.1 

1.6 

1.5 

2.0 

Himalayan-Flemish. 

9.8 

7.3 

4.8 

7.0 

9.7 

10.6 

8.2 

Polish-Flemish  

4.7 

5.2 

5.3 

5.6 

21.0 

21.2 

10.5 

|J  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

TABLE  32. — Comparative  »ize  of  the  two  sexes  in  the  several  groups  of  cross-bred  rabbits. 


Group. 

Tibia. 

Femur. 

Humerus. 

Skull-length. 

Males. 

Females. 

Males. 

Females. 

Males. 

Females. 

Males. 

Females. 

t  i 

c 

| 

6 

1 

1 

a 

i 

6 
y. 

1 

a 
y. 

i 

0 

1 

c 

y. 

1 

Fi  PXH 

15    93.65 
24    90.07 
8100.20 
33    97.78 
14    96.59 
65   94.29 

10 
:50 
9 
88 
18 

1,2 

91.65 
89.68 
97.90 
96.88 
95.75 
92    1  1 

15 
24 

a 

5:5 
11 

M 

78.78 
76.45 
87.95 
84.90 
83.52 
80.87 

10 
80 
9 
88 
18 

62 

77.45 
75.97 
86.68 
84.63 
83.15 
79.53 

15 

22 
8 
53 
14 
05 

63.53 
61.15 
69.45 
67.36 
66.41 
64.03 

10 
29 
9 
•5:5 
13 
01 

62.20 
60.73 
68.26 
67.33 
65.93 
63.88 

15 
23 

52 
11 

15 

70.50 
69.18 
79.48 
76.37 
75.59 
73.14 

10 

30 

9 

152 
13 
80 

69.95 
68.80 
78.58 
76.66 
75.50 
73.12 

F,.PXH  

FI.  HXF  

Ft.  H  XF  
F,.  PXF  
Ft.  PXF  

Weighted  mean*. 
Per  cent  greater. 

94.72 
1.58 

93.24 

81.35 
1.10 

80.46 

64.66 
0.57 

64.29 

73.42 
0.16 

73.30 

Anterior 
skull-width. 

Posterior 
skull-width. 

Ear-length. 

Weight. 

Group. 

Males. 

Females. 

Males. 

Females. 

Males. 

Females. 

Males. 

Females. 

I 

1 

1 

c 

1 

4 

1 

d 

1 

d 

y. 

I 

6 

z 

1 

| 

1 

F,.  PXH  ] 
F^PXH  S 
Fi.HXF  
F,,  H  XF  i 
F,.  PXF  1 
F,,  PXF  ( 

5159  90 
«  38.  65 
843.63 
1141.91 
442.48 
(441.28 

10 
.'51 
9 
83 
13 
01 

38.65 
37.94 
42.36 
41.38 
42.13 
40.32 

15 
2.'5 
8 
51 
11 
64 

40.23 
38.61 
43.88 
42.49 
42.84 
41.20 

10 
29 
1 

33 
18 

01 

38.35 
37.90 
42.70 
41.50 
41.58 
40.38 

15 
24 
8 

•57 
14 
07 

9 
9 

11 
11 
10 
10 

54 
.25 
.45 
50 
.91 
6» 

10 
31 
9 
'53 
13 
04 

9.42 
9.16 
11.66 
11.65 
10.97 
10.71 

15 
28 

x 

50 
14 
il 

1, 
1. 
2, 
2. 

2, 
2, 

957 
500 
094 
401 
«'.!» 
(WO 

K 
27 
8 
32 
18 

52 

to  to  to  to  •->  to 

005 
704 
886 
531 
545 
176 

Weighted  mean* 
Per  cent  greater. 

41.05 
2.03 

40.23 

41 
2 

21 
40 

40.22 

10 

55 

10 
0 

.5H 
.20 

2, 

110 

2, 

221 
5.26 

•  The  weighted  means  were  obtained  by  counting  each  male  mean  the  same  number  of  times 
as  each  female  mean,  the  number  of  individuals  assumed  for  the  purpose  of  the  computation 
to  occur  in  each  sex  of  each  gioup  being  as  follows:  FI,  PXH,  15;  F»,  PXH,  30;  Fi,  H  XF,  10; 
F,,  HXF.  33;  F,,  PXF.  15;  F,.  PXF.  66. 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


43 


TABLE  33. — Descriptive  list  of  rabbits  studied. 

Abbreviations  in  column  headed  "color":  A,  snow-white  albino;  An,  angora;  B,  black;  Dil, 
dilute;  G,  gray;  H,  Himalayan  albino;  St.  G,  steel  gray;  Y,  yellow.  Measurements  in  milli- 
meters; weight  in  grams. 

I.   POLISH,  ALL  SNOW-WHITE  ALBINOS. 


Designation. 

Mother. 

Father. 

Born. 

-3 

MI 

3 
ja 

CQ 

Anterior  skull- 
width. 

Posterior  skull- 
width. 

3 
1 

| 

W 

1 

1 

91  
92  
99  

910  

92413  
92712  
92713  
92738  
9  2753  
93186 

1 
10 
10 
2 
9 
2738 
2738 
2753 
2753 
2753 

3 
3 
3 
3 
3 
3 
3 
3 
3 
3 

June  11,  1917 
Sept.  10,  1917 
Do. 
Sept.  13,  1917 
Sept.  20,  1917 
June  14,  1918 
Do. 
Aug.  16,  1918 
Do. 
Do. 

68.9 
68.4 
68.2 
65.5 
65.4 
66.2 

63  .6 
63.6 
69.3 
65.0 

65*6 
67.0 
63.4 
65.5 
67.1 
64.5 
64.6 

37.3 
38.6 
38.4 
37.8 
36.2 
36.5 

36.5 
37.5 
41.0 
39.6 

39.2 
37.9 
38.7 
38.2 
36.8 
38.9 
38.8 

37.8 
38.5 
38.4 
38.8 
37.5 
37.8 

37*8 
37.4 
40.5 
38.4 

38^9 
37.7 
38.7 
38.3 
37.1 
37.3 
39.6 

75.4 
73.1 
73.4 
73.9 
68.4 
70.5 
71.0 
71.5 
69.9 
76.4 
73.2 

72.5 
73.0 
72.9 
71.0 
73.3 
73.6 
72.8 

8e'4 

84.7 
86.0 
84.9 
80.1 
80.7 
81.4 
84.5 
79.9 
89.6 
84.2 

83.6 
87.6 
82.7 
82.3 
83.6 
84.5 
85.0 

59^3 
57.1 
58.8 
60.3 
55.5 
57.0 
57.3 
58.2 
56.7 
60.9 
57.5 

57^2 
58.8 
57.7 
57.7 
57.6 
57.5 
58.8 

8.4 
8.3 
8.4 
8.7 
8.3 
8.1 
8.7 
8.1 
8.5 
8.2 
8.5 
8.4 
8.4 
8.4 
8.4 
8.2 
8.2 
8.1 
8.4 
8.4 
8.2 

1.275 
1,425 
1,545 
1,575 
1,250 
1.355 
1,295 

1^230 
1.280 
1.700 
1.450 

1^505 
1,400 
1.450 
1.450 
1,200 
1,340 
1.325 

93187  
93488  
9  3489  
93490  

o*3 

0*2312  
0*2313  
0*2314  
o"2412  
0*2741  
0*2742  
0*2751  
0*3318  
o"3487  
0*3561  

10 
10 
10 

1 
2 
2 
9 
2713 
2753 
2712 

3 
3 
3 
3 
3 
3 
3 
3 
3 
3 

May  28,  1917 
Do. 
Do. 
June  11,  1917 
Sept.  13,  1917 
Do. 
Sept.  20,  1917 
June  17,  1918 
Aug.  16,  1918 
Aug.  21,  1918 

II.   HIMALAYAN,  ALL  "HIMALAYAN"  ALBINOS. 


i 

"5 

.M 

]j 

Designation. 

1 

| 

Born. 

I 

l| 

ll 

s 

S 

1 

I 

«> 

1 

1 

i 

<    * 

£* 

B 

= 

£ 

i 

94      

66  1 

35  8 

37  3 

77.3 

92.9 

61   .". 

96  

72.9 

39.6 

40.2 

K2.S 

95.9 

63.9 

9.7 

2.210 

92206  

4 

5 

Apr.  27,  1917 

69.1]37.3 

37.4 

79.3 

94.3 

62.4 

9.2 

2,085 

92210  

4 

5 

Do. 

69.0137.3 

38.0 

80.7 

94.8 

63.8 

9.5 

1,835 

9  3565  

2210 

2208 

Aug.  21,  1918    67.5|35.9 

37.4 

77.8 

92.1 

63.9 

9.5 

1,620 

93566  

2210 

2208 

Do.             66.9135.3 

.    72  1  37  3 

37.1 
37  4 

77.0 
81.3 

92.9 
96.0 

62.8 
ft?  9 

9.6 

1,600 

c?2208  

4 

5 

Apr.  27.1917    69.138.2 

39.2 

80.0 

93.0163.6 

9.4 

1.850 

1        ] 

| 

44 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


TABLE  33.— Descriptive  list  of  rabbits  studied— Continued. 
III.   FLIMIBH  GIANT. 


Designa- 
tion. 

, 

| 

j 

Born. 

1 

Anterior  skull- 
width. 

Posterior  skull- 
width. 

£ 

1 

H 

1 

1 

9B 
97 
cfA 
<72 
c?2681 

B 

StG 
StG 
StG 
StG 

82.9 
87.1 
88.2 
84.6 
85.6 

44.5 
45.4 
46.7 
43.8 
47.4 

44.7 
44.0 
47.4 
44.9 
46.4 

95.3 
97.8 
102.6 
94.1 
98.5 

106.7 
113.1 
116.4 
105.2 
113.5 

73.1 
75.6 

73^4 
77.9 

14.7 

14'e 
14.3 

4,060 

3^480 
3,400 

'Sept."8.'l917 

9B 

rf2 

IV.   Fi,  POLISH X HIMALAYAN,  ALL  "HIMALAYAN"  ALBINOS. 


Designation. 

Mother. 

1 
1 

Born. 

Skull-length 

Anterior  skull- 
width. 

Posterior  skull- 
width. 

j 

.2 

.0 

W 

1 

1 

92317  
92320  

9P 
9P 
4H 
2P 
2P 
6H 
10P 
2206  H 
2210  H 
2210H 
9P 
9P 
9P 
4H 
4H 
4H 
2P 
2P 
2P 
6H 
6H 
6H 
6H 
6H 
2210H 

5H 
5H 
3P 
5H 
5H 
3P 
5H 
3P 
3P 
3P 
5H 
5H 
5H 
3P 
3P 
3P 
5H 
5H 
5H 
3P 
3P 
3P 
3P 
3P 
3P 

May  28,  1917 
Do. 
Do. 
May  29,  1917 
Do. 
June    4,1917 
June  28,  1917 
Apr.  27,  1918 
Do. 
Do. 
May  28,  1917 
Do. 
Do. 
May  28,  1917 
Do. 
Do. 
May  29,  1917 
Do. 
Do. 
June    4,  1917 
Do. 
Do. 
Do. 
Do. 
Apr.  27,  1918 

74.8 
72.3 
70.5 
70.5 
70.8 
68.7 
70.7 
62.1 
67.8 
71.4 
74.5 
70.4 
72.7 
69.0 
71.0 
71.7 
68.1 
68.5 
70  9 
68.5 
71.3 
70.6 
70.8 
70.7 
68.4 

39.9 
39.6 
38.7 
38.8 
39.8 
38.5 
38.7 
37.0 
36.9 
38.8 
41.0 
39.0 
40.2 
39.4 
40.7 
40.9 
39.4 
38.9 
40  4 
41.8 
40.9 
39.3 
39.9 
40.6 
38.4 

38.6 
38.5 
38.5 
39.4 
39.6 
38.2 
36.8 
37.3 
37.5 
38.7 
40.2 
38.8 
40.0 
39.6 
40.9 
40.6 
40.2 
37.8 
40  5 
42.7 
41.4 
39.4 
40.7 
41.0 
39.9 

79.0 
78.6 
79.0 
76.9 
77.8 
78.5 
78.4 
73.9 
75.4 
77.9 
79.9 
78.4 
78.0 
77.9 
79.7 
82.0 
76.5 
75.5 
77.3 
78.9 
81.9 
78.7 
80.5 
80.7 
77.4 

95.4 
93.2 
93.7 
91.7 
92.7 
91.9 
91.5 
86.0 
89.2 
91.8 
96.5 
92.9 
93.4 
93.9 
96.8 
96.8 
91.2 
90.3 
92.7 
91.7 
96.8 
92.9 
94.0 
95.5 
91.6 

64.7 
63.3 
63.7 
62.2 
63.0 
62.5 
61.6 
59.3 
60.7 
60.9 
64.6 
63.0 
62.8 
62.6 
63.7 
65.1 
62.7 
61.9 
62.4 
62.4 
64.5 
62.6 
63.7 
63  8 
62.8 

9.6 
9.4 
9.6 
9.5 
9.7 
9.5 
9.2 

9.4 
9.3 
9.7 
9.5 
9.3 
9.5 
9.5 
9.7 
9.4 
9.4 
98 
9.4 
9.7 
9.6 
9.5 
9.5 
9.6 

2,270 
2,285 
1,940 
2,390 
2.495 
1,940 
1.675 

l!540 
1,825 
2,145 
1.945 
1,770 
1.835 
1,920 
2.060 
1,945 
1.945 
2,110 
2,175 
2,045 
1.865 
1.870 
2,000 
1.735 

9  2323 

92340  . 

92341 

92395  
92446  

93094  

93099  
93100  
c?2316  
d"2318  
d"2319  
d"2321  
d"2322  
d"2324  
c?2342  
d"2343  
d"2344  
c?2391  
tf2392 

cf2393  
d"2394  

rf2396  
d*3101 

GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


45 


TABLE  33.— Descriptive  list  of  rabbits  studied— Continued. 
V.   Fi,  POLISH  X  FLEMISH. 


Designa- 
tion. 

Color. 

1 

1 

Born. 

•C3 

-2 

"3 
QQ 

terior  skull- 
dth" 

<e 

I 

i 

o 

1 

1 

02 

1? 

" 

(2 

'£ 

K 

1 

I 

92430 

G 

7F 

3P 

June  29,  1917 

74.6 

42.8 

41.8 

86.2 

99.1 

66.0 

11.1 

2,680 

92431 

StG 

7F 

3P 

Do. 

74.7 

41.8 

42.7 

81.8 

92.1 

64.9 

11.2 

2.500 

92432 

B 

7F 

3P 

Do. 

77.0 

42.3 

42.8 

83.3 

96.8 

65.0 

11.2 

2.500 

92436 

G 

7F 

3P 

Do. 

74.3 

42.1 

40.5 

84.1 

98.5 

65.8 

10.3 

2,300 

92437 

G 

7F 

3P 

Do. 

76.3 

42.4 

41.8 

83.7 

96.8 

65.0 

11.0 

2.500 

92451 

G 

9P 

2F 

July     7,  1917 

76.3 

42.8 

41.5 

83.3 

96.8 

67.9 

11.0 

2,300 

92474 

B 

BF 

3P 

July     8,  1917 

74.5 

40.0 

39.7 

83.7 

95.9 

66.6 

11.3 

2.055 

92507 

StG 

2P 

2F 

July  19,  1917 

75.3 

42.4 

41.7 

81.7 

93.7 

65.8 

11.1 

2.730 

92508 

StG 

2P 

2F 

Do. 

74.4 

41.6 

42.3 

81.5 

94.0 

65.4 

11.3 

2,715 

92509 

StG 

2P 

2F 

Do. 

76.0 

42.0 

40.9 

82.8 

97.0 

65.3 

11.1 

2,545 

92510 

StG 

2P 

2F 

Do. 

75.7 

43.2 

42.3 

82.9 

94.4 

66.8 

10.8 

2,890 

92511 

StG 

2P 

2F 

Do. 

76.3 

41.9 

41.4 

82.3 

93.7 

66.8 

10.9 

2,660 

92576 

G 

IP 

2F 

July  26,  1917 

76.2 

42.8 

41.7 

84.0 

96.0 

66.4 

10.3 

2,720 

c?2429 

G 

7F 

3P 

June  29,  1917 

74.7 

41.2 

41.5 

81.8 

96.2 

63.7 

10.3 

2,385 

0*2433 

StG 

7F 

3P 

Do. 

76.9 

43.7 

43.9 

85.4 

99.9 

67.5 

11.0 

2.735 

0^2434 

B 

7F 

3P 

Do. 

76.2 

41.8 

43.0 

84.9 

98.7 

66.7 

10.8 

2.525 

0^2435 

G 

7F 

3P 

Do. 

74.3 

42.5 

42.8 

85.8 

100.2 

67.0 

10.6 

2.526 

0*2454 

StG 

9P 

2F 

July     7,  1917 

75.8 

41.7 

42.6 

84.8 

100.5 

67.3 

11.6 

2,380 

0*2473 

B 

BF 

3P 

July     8,  1917 

79.8 

44.4 

44.4 

86.7 

98.7 

68.5 

11.4 

2.670 

cf2506 

StG 

2P 

2F 

July  19,  1917 

73.8 

42.6 

43.0 

80.1 

92.7 

64.1 

10.3 

2,350 

0"2577 

StG 

IP 

2F 

July  26,  1917 

77.2 

42.2 

41.9 

84.0 

96.2 

66.8 

11.0 

2,500 

0*2578 

StG 

IP 

2F 

Do. 

73.0 

42.3 

42.0 

82.1 

94.5 

64.4 

10.3 

2,160 

0*2650 

G 

9P 

2F 

Aug.    9,1917 

75.5 

42.7 

42.8 

82.0 

95.4 

65.5 

11.0 

2,500 

0*2834 

G 

10P 

2F 

Dec.    7,  1917 

75.9 

43.1 

42.6 

85.2 

96.2 

67.1 

10.7 

2,445 

0*2865 

G 

2P 

2F 

Dec.    9,  1917 

75.5 

42.8 

44.1 

83.9 

94.7 

67.8 

11.4 

2,400 

CJ*2866 

G 

2P 

2F 

Do. 

75.0 

41.8 

42.5 

82.8 

95.3 

66.7 

11.4 

2.650 

0*2867 

StG 

2P 

2F 

Do. 

74.6 

42.0 

42.1 

80.7 

93.2 

66.1 

10.9 

2.350 

VI.   Fi,  HIMALAYAN  XFLEMISH. 


f' 

| 

| 

Designa- 
tion. 

Color. 

1 

1 

Born. 

„ 

3 

11 

•S  -o 

1 

i 

1 

i 

S 

i 

a 

<! 

&  * 

t 

P 

1 

W 

* 

92517 

StG 

4H 

2F 

July  19.1917 

76.4 

42.4 

42.9 

86.6 

99.8 

69.3 

11.8 

3,040 

92519 

G 

4H 

2F 

Do. 

78.7 

42.8 

43.4 

85.1 

97.5 

67.0 

11.8 

2.800 

92521 

G 

4H 

2F 

Do. 

80.0 

43.1 

42.1 

88.4 

102.1 

71.1 

11.5 

3,060 

92642 

StG 

6H 

2F 

Aug.    9,  1917 

79.5 

42.8 

43.5 

88.7 

99.7 

69.0 

11.8 

2,800 

92645 

StG 

6H 

2F 

Do. 

78.8 

43.5 

42.7 

86.5 

96.8 

67.0 

11.8 

2,800 

92646 

G 

6H 

2F 

Do. 

81.5 

43.4 

43.2 

86.2 

97.2 

67.8 

11.6 

2,765 

92828 

StG 

6H 

2F 

Dec.     7,  1917 

76.3 

41.8 

40.9 

84.8 

95.0 

66.2 

11.3 

2,775 

92830 

G 

6H 

2F 

Do. 

79.9 

42.3 

43.7 

88.7 

97.8 

68.411.9 

3,050 

92832 

StG 

6H 

2F 

Do. 

76.3 

39.7 

42.0 

85.0 

95.5 

68  3 

11.5 

0*2518 

G 

4H 

2F 

July  19,  1917 

78.6 

42.3 

43.1 

88.1 

99.9 

71.011.3 

2^440 

0*2520 

StG 

4H 

2F 

Do. 

77.6 

43.8 

44.2 

86.8 

100.9 

69.1 

11.5 

2.775 

0*2522 

G 

4H 

2F 

Do. 

79.6 

44.6 

44.1 

88.4 

101.0 

69.4 

11.7 

2.875 

0*2643 

StG 

6H 

2F 

Aug.    9,  1917 

82.8 

46.3 

44.4 

91.9 

105.0 

70.9 

11.4 

2.900 

0*2644 

StG 

6H 

2F 

Do. 

79.3 

41.7 

43.9 

86.2 

98.1 

68.8 

11.4 

2.550 

0*2647 

G 

6H 

2F 

Do. 

80.4 

43.2 

44.0 

88.2 

99.0 

68.611.7 

2.600 

0*2648 

G 

6H 

2F 

Do. 

44.5 

44.6 

87.4 

98.6 

68  711.4 

2.665 

0*2649 

G 

6H 

2F 

Do. 

78^2 

42.7 

43.0 

86.8 

98.9 

69.311.2 

2.750 

GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


TABLE  33.— Descriptive  litt  of  rabbits  studied— Continued. 

VII.     Fj,    POLISH  XHlMALAYAN. 


De«cn»- 

tion. 

Color. 

j 

j 

Born. 

Skull-length. 

Anterior  skull- 
width. 

1  Posterior  skull- 
width. 

1 

t 

K 

1 

*» 

1 

92915 

H 

2323 

2324 

Apr.  16,  1918 

68.9 

38.1 

38.4 

77.7 

90.7 

61.5 

9.5 

1.880 

92916 

A 

2323 

2324 

Do. 

65.6 

35.5 

36.5 

74.6 

87.6 

58.5 

9.1 

1.230 

92993 

H 

2446 

2342 

Apr.  18,  1918 

65.3 

36.4 

74.4 

87.4 

60.6 

8.8 

93028 

A 

2320 

2316 

Apr.  21,  1918 

75.0 

39.5 

38!7 

80.2 

96.2 

63.9 

9.5 

1.800 

93029 

A 

2320 

2316 

Do. 

69.1 

37.8 

37.5 

75.7 

91.4 

61.2 

9.2 

1.515 

93173 

H 

2320 

2316 

June  14.  1918 

70.3 

».p»   ! 

35.7 

78.7 

91.4 

62.1 

9.5 

1.490 

93426 

H 

2317 

2316 

July     4,  1918 

72.6 

36.5 

36.9 

77.8 

91.0 

62.1 

9.5 

1.425 

93427 

H 

2317 

2316 

Do. 

67.7 

36.9 

37.0 

76.7 

91.0 

62.0 

9.2 

93428 

H 

2317 

2316 

Do. 

72.5 

38.4 

37.8 

76.6 

90.7 

61.5 

9.1 

1.685 

93544 

A 

2323 

2324 

Aug.  15,  1918 

70.4 

39.2 

39.5 

79.3 

92.7 

64.5 

9.5 

1.700 

93545 

A 

2323 

2324 

Do. 

70.1 

40.0 

:w  ( 

80.5 

94.3 

64.9 

9.7 

1,980 

93610 

H 

2446 

2316 

Sept.    1,  1918 

69.6 

36.9 

36.9 

75.7 

89.0 

60.8 

8.8 

1.750 

93611 

H 

2446 

2316 

Do. 

65.3 

37.3 

37.3 

73.3 

86.4 

58  .  : 

8.5 

93629 

H  (Blue) 

2320 

2344 

Nov.    2,  1918 

71.6 

40.5 

39.2 

77.8 

92.7 

61.5 

8.9 

2^170 

93633 

H  (Blue) 

2320 

2344 

Do. 

67.2 

37.4 

37.8 

76.7 

92.7 

62.4 

9.1 

1.705 

93634 

A 

2320 

2344 

Do. 

70.6 

39.6 

39.3 

76.9 

91.4 

63.1 

9.2 

1.715 

93637 

H  (Blue) 

2317 

2344 

Do. 

69.1 

39.9 

39.4 

78.7 

92.7 

63.7 

9.9 

2,325 

93638 

H 

2317 

2344 

Do. 

70.4 

36.8 

37.1 

77.7 

92.8 

62.4 

9.1 

1.900 

93641 

A 

2317 

2344 

Do. 

8.9 

94079 

H 

2323 

2324 

Apr.     3,  1919 

67^2 

38^5 

37.6 

76~9 

89^4 

60.5 

9.8 

1.466 

94193 

H 

3094 

2324 

May  26,  1919 

70.2 

39.7 

38.1 

77.2 

90.6 

61.8 

9.8 

1.985 

94194 

A 

3094 

2324 

Do. 

69.6 

38.9 

as.  6 

77.3 

89.8 

61.9 

9.2 

1.810 

94196 

H 

3099 

2324 

Do. 

68.8 

39.3 

38.5 

77.5 

90.9 

9.8 

1,615 

94201 

A 

2320 

2344 

June    3,  1919 

66.0 

36.5 

37.3 

68.4 

80.4 

54.6 

8.3 

1,520 

94202 

A 

2320 

2344 

Do. 

68.9 

38.4 

39.3 

73.4 

86.5 

57.6 

9.0 

1,865 

94204 

H 

2320 

2344 

Do. 

65.5 

37.9 

37.3 

73.0 

85.8 

58.3 

8.7 

1,600 

94205 

H 

2320 

2344 

Do. 

65.9 

36.0 

36.6 

74.1 

88.0 

56.5 

8.8 

1,620 

94207 

H 

2320 

2344 

Do. 

68.2 

37.5 

38.8 

74.3 

86.4 

59.5 

9.2 

1.825 

94208 

H 

2320 

2344 

Do. 

67.2 

38.1 

37.7 

69.8 

82.3 

54.9 

8.9 

1.530 

94270 

H 

2323 

2324 

July  25,  1919 

65.4 

37.2 

37.1 

75.0 

89.4 

60.2 

8.7 

1.300 

94333 

A 

2446 

2344 

July  26,  1919 

69.5 

37.9 

37.8 

75.6 

89.5 

59.5 

8.8 

1.600 

c?3170 

H 

2320 

2316 

June  14,  1918 

68.8 

37.5 

36.7 

74.8 

88.2 

60.4 

9.7 

1,340 

(73171 

H 

2320 

2316 

Do. 

68.8 

38.0 

38.2 

76.0 

89.4 

60.3 

8.9 

1,395 

<f3172 

H 

2320 

2316 

Do. 

78.2 

88.0 

9.4 

d"3231 

H 

2395 

2324 

Do. 

68^9 

38.5 

38.9 

74.6 

86.3 

59.8 

9.2 

1.505 

tf3429 

H 

2317 

2316 

July     4,  1918 

71.7 

40.0 

39.5 

77.0 

92.0 

62.3 

9.5 

1.655 

C73642 

A 

2323 

2324 

Aug.  15,  1918 

66.1 

38.7 

38.9 

76.6 

90.6 

60.2 

9.0 

1,630 

0"3643 

H 

2323 

2324 

Do. 

69.6 

39.8 

40.0 

79.6 

94.6 

63.6 

9.4 

1.620 

<f3609 

H 

2446 

2316 

Sept.    1,  1918 

71.1 

40.0 

39.7 

78  0 

90.4 

61.7 

9.3 

1.910 

rf3630 

A 

2320 

2344 

Nov.    2,  1918 

71.5 

38.5 

38.2 

80.1 

94.3 

63.9 

9.4 

1.820 

<f3632 

H 

2320 

2344 

Do. 

70.9 

39.2 

38.9 

78.6 

94.2 

63.2 

9.3 

1.770 

d<3636 

H 

2317 

2344 

Do. 

67.6 

37.4 

37.3 

77.0 

93.5 

62.9 

9.2 

1.410 

<f303G 

H 

2317 

2344 

Do. 

70.8 

39.5 

W.4 

77.8 

93.5 

63.7 

9.2 

1,585 

<f3639 

H 

2317 

2344 

Do. 

71.6 

39.7 

38.8 

78.4 

94.1 

63.8 

9.7 

1.720 

(73640 

A 

2317 

2344 

Do. 

72.0 

40.5 

40.4 

78.6 

93.4 

63.7 

9.4 

,890 

(74196 

B 

3094 

2324 

May  26,  1919 

67.3 

36.9 

5.9 

73.5 

86.9 

58.7 

9.1 

.390 

(74199 

H 

3099 

2324 

Do. 

69.0 

38.6 

7.4 

76.6 

90.6 

62.4 

8.9 

,375 

(74203 

A 

2320 

2344 

June    3,  1919 

67.6 

38.9 

8.6 

73.3 

85.7 

58.2 

9.3 

.610 

c'41'Wi 

H 

2320 

2344 

Do. 

68.2 

40.2 

9.6 

72.3 

83.7 

56.7 

9.5 

,600 

(74209 

H 

2320 

2344 

Do. 

68.3 

so 

8.7 

73.7 

86.6 

58.2 

9.3 

,435 

cTOU 

H  (Blue) 

2323 

2324 

July  25,  1919 

68.8 

9.4 

8.4 

78.8 

91.5 

9.0 

,510 

MM 

A 

2323 

2324 

Do. 

71.1 

9.2 

00 

78.7 

94.2 

62^6 

9.7 

,500 

u'4l!«9 

H 

2323 

2324 

Do. 

65.0 

6.3 

6.0 

73.1 

84.9 

60.8 

8.4 

,090 

(74332 

A 

2446 

2344 

June  26,  1919 

67.9 

6.8 

6.4 

74.0 

86.8 

59.8 

8.9 

,400 

(74334 

A 

2446 

2344 

Do. 

69.0 

B.I 

83 

75.3 

88.8 

9.5 

9.3 

,715 

GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


47 


TABLE  33. — Descriptive  list  of  rabbits  studied — Continued. 
VIII.   Fj,  POLISH  XFLEMISH. 


Designa- 
tion. 

Color. 

i 

£ 

Born. 

Skull-length. 

Sj 

11 
3* 

Posterior  skull-  1 
width. 

£ 

05 

a 

S 

Humerus. 

1 

Weight. 

92908 

A 

2436 

2434 

Apr.  16,  1918 

76.3 

41.7 

39.6 

K3.4 

95.5 

63.7 

10  0 

2,060 

92909 

Y 

2436 

2434 

Do. 

10.4 

92918 

B 

2509 

2506 

Apr.  17.  1918 

71.6 

41.6 

41^6 

80^3 

92.8 

63^8 

11.1 

2^490 

92920 

StG 

2509 

2506 

Do. 

70.5 

39.5 

40.2 

80.0 

93.7 

64.8 

11.3 

92929 

StG 

2451 

2506 

Do. 

72.8 

41.5 

40.8 

K0.3 

91.6 

64.6 

10.7 

2^400 

92932 

A 

2451 

2506 

Do. 

73.3 

40.3 

40.2 

79.3 

92.5 

65.3 

10.5 

2.430 

92943 

B  An 

2430 

2434 

Do. 

75.6 

40.5 

38.6 

82.3 

96.8 

65.3 

11.6 

2,150 

93002 

B 

2576 

2506 

Apr.  19,  1918 

74.5 

41.7 

41.7 

83.2 

95.2 

66.4 

11.9 

93004 

A 

2576 

2506 

Do. 

73.0 

40.9 

39.8 

79.0 

91.8 

64.0 

9.8 

2,055 

93008 

StG 

2510 

2506 

Do. 

73.0 

40.0 

38.7 

79.6 

90.7 

63.2 

10.8 

93009 

G 

2510 

2506 

Do. 

67.9 

39.5 

39.7 

77.7 

90.2 

63.3 

10.3 

93010 

Blue  G 

2510 

2506 

Do. 

73.5 

41.6 

40.7 

77.4 

92.1 

63.4 

11.2 

2^365 

93011 

St  Blue 

2510 

2506 

Do. 

77.2 

41.4 

40.7 

79.1 

91.9 

63.7 

10.8 

2.175 

93108 

StG 

2474 

2473 

May    6,  1918 

73.9 

39.3 

38.8 

80.6 

92.8 

62.9 

10.2 

1.900 

93111 

StG 

2474 

2473 

Do. 

70.8 

39.0 

38.7 

79.4 

92.6 

63.7 

10.1 

1.765 

93112 

Blue 

2474 

2473 

Do. 

73.3 

40.0 

38.9 

77.7 

89.7 

63.2 

11.1 

2.150 

93159 

A 

2511 

2506 

June  14,  1918 

65.9 

37.9 

38.8 

72.9 

85.0 

58.1 

9.7 

93160 

StG 

2511 

2506 

Do. 

72.6 

40.4 

42.5 

77.7 

87.8 

63.4 

10  9 

2^440 

93162 

StG 

2511 

2506 

Do. 

75.6 

40.8 

40.8 

83.7 

95.3 

67.3 

11.8 

2,460 

93192 

StG 

2430 

2434 

June  14,  1918 

67.0 

37.5 

37.1 

74.6 

87.0 

58.1 

9.6 

1,760 

93195 

G 

2430 

2434 

Do. 

74.2 

40.7 

40.7 

83.8 

99.0 

65.8 

10.8 

2,420 

93201 

A 

2576 

2506 

Do. 

72.8 

40.5 

40.4 

80.0 

89.8 

62.1 

10.2 

2,340 

93209 

A 

2509 

2506 

Do. 

71.9 

40.3 

39.9 

74.6 

86.5 

61.3 

10.4 

1,950 

93210 

StG 

2509 

2506 

Do. 

70.9 

40.3 

41.7 

75.2 

85.4 

60.7 

11.1 

2.070 

93212 

B 

2509 

2506 

Do. 

70.3 

40.8 

40.7 

82.1 

94.7 

65.5 

11.1 

93240 

G 

2451 

2506 

June  15,  1918 

63.7 

38.7 

39.5 

72.8 

82.8 

58.5 

9.9 

1.700 

93301 

StG 

2436 

2434 

June  16,  1918 

75.0 

41.6 

41.3 

82.9 

94.9 

65.9 

10.2 

2.670 

93370 

A 

2437 

2434 

July   18,  1918 

77.5 

42.0 

40.8 

81.9 

94.5 

64.5 

10  8 

2,050 

93371 

A 

2437 

2434 

Do. 

72.7 

38.9 

39.9 

78.0 

90.1 

61.7 

10.7 

2,050 

93377 

St  Blue 

2508 

2506 

July  20,  1918 

73.0 

40.0 

40.7 

77.3 

91.0 

62.9 

10.6 

1,810 

93379 

B 

2508 

2506 

Do. 

69.6 

38.7 

39.8 

76.8 

88.9 

64.3 

9.8 

1.840 

93397 

B 

2510 

2506 

July  23,  1918 

77.4 

42.0 

42.3 

82.0 

95.0 

67.1 

10.8 

2.325 

93421 

Blue 

2474 

2473 

July     4,  1918 

71.2 

39.5 

39.8 

81.1 

94.8 

66.7 

10.6 

2.075 

93423 

StG 

2474 

2473 

Do. 

75.8 

40.3 

40.3 

84.7 

99.0 

68.7 

11.1 

2.140 

93447 

A 

2451 

2506 

Aug.  16,  1918 

76.3 

42.2 

41.3 

78.2 

89.8 

64.0 

11.2 

2,200 

93450 

St  G 

2451 

2506 

Do. 

93476 

A 

2576 

2506 

Do! 

9.8 

93479 

G 

2576 

2506 

Do. 

9.7 

93511 

A 

2509 

2506 

Do. 

75.5 

42'3 

43  '3 

78.9 

88.5 

62.9 

11.1 

2,475 

93513 

StG 

2509 

2506 

Do. 

70.8 

37.6 

40.9 

76.0 

87.7 

63.4 

10.7 

1.795 

93527 

StG 

2511 

2506 

Do. 

77.0 

41.8 

41.8 

82.6 

93.8 

65.7 

11.1 

2.675 

93528 

B 

2511 

2506 

Do. 

76.2 

41.8 

41.2 

82.8 

95.8 

66.8 

10.9 

2.250 

93531 

A 

2511 

2506 

Do. 

77.3 

41.0 

42.0 

83.5 

97.6 

67.5 

11.9 

2.525 

93532 

A 

2511 

2506 

Do. 

73.3 

40.0 

41.0 

77.5 

87.8 

«1    4 

10.2 

2.360 

93560 

StG 

2507 

2506 

Aug.  20,  1918 

74.7 

42.3 

41.1 

77.8 

89.4 

63.6 

11.2 

2.170 

93652 

A 

2510 

2506 

Nov.    2,  1918 

37.8 

37.9 

77.2 

89.2 

63.2 

10  7 

93654 

StG 

2510 

2506 

Do. 

72.7 

38.4 

40.1 

76.7 

89.1 

62  .  5 

10.3 

2^050 

93655 

StG 

2510 

2506 

Do. 

79.9 

92.1 

10.9 

93657 

A 

2436 

2434 

Do. 

79.0 

40.8 

40.4 

87.6 

103.0 

70.0 

11.3 

2^380 

93658 

A 

2436 

2434 

Do. 

72.7 

41.4 

42.0 

80.5 

93.6 

63.0 

10.1 

2.260 

93659 

StG 

2436 

2434 

Do. 

75.6 

42.4 

41.8 

85.6 

100.6 

67.1 

10.7 

2.645 

93661 

A  An 

2432 

2434 

Do. 

78.8 

40.6 

40.4 

88.3 

102.0 

fi9.4 

11.4 

2,500 

93663 

A 

2432 

2434 

Do. 

79.3 

42.3 

41.4 

87.5 

102.8 

68  .  7 

10  9 

2,630 

93826 

Blue 

2474 

2473 

Feb.  25,  1919 

74.3 

41.5 

39.9 

82.2 

96.4 

05  -  9 

11.5 

2.190 

93836 

G 

2511 

2866 

Do. 

75.0 

39.3 

41.0 

77.3 

91.8 

64.1 

10.9 

2.125 

48  GENETIC  STUDIES  OF  RABBITS  AND   RATS. 

TABLE  33.— Descriptive  list  of  rabbits  studied-Continued. 
VIII.   F,,  POLISH  X FLEMISH— Continued. 


Uun.' 

Color. 

s 

| 

Born. 

Skull-length. 

Anterior 
1  Bkull-width. 

1  .Posterior 
skull-width. 

Femur. 

P 

H 

1 

1 

93839 

A 

2451 

2866 

Feb.  27,  1919 

J7.7 

9.3 

0.0 

72.5 

85.1 

8.7 

0.2 

.710 

93843 

Q 

2451 

2866 

Do. 

re.  8 

10.4 

0.1 

81.0 

92.3 

55.9 

1.3 

,315 

93850 

B 

2576 

2866 

Feb.  25,  1919 

r4.6 

1.0 

1.3 

80.0 

90.9 

2.6 

0.5 

.255 

93852 

Blue 

2576 

2866 

Do. 

59.8 

0.6 

9.5 

76.4 

89.1 

1.4 

0.3 

,770 

93858 

StG 

2510 

2866 

Do. 

73.8 

0.4 

0.5 

82.4 

93.5 

6.3 

1.3 

,130 

93883 

B 

2509 

2866 

Do. 

58.5 

7.2 

0.0 

73.1 

82.5 

7.5 

0.0 

,780 

93884 

B 

2509 

2866 

Do. 

58.7 

8.3 

9.7 

75.8 

88.3 

0.6 

0.8 

.765 

9  3v* 

luGAn 

2436 

2434 

Do. 

70.1 

9.6 

tO.  3 

82.0 

95.2 

5.0 

0.5 

,920 

94039 

B 

2511 

2866 

May    5.  1919 

70.0 

8.7 

9.8 

80.7 

93.1 

64.5 

0.6 

94067 

Blue 

2431 

2433 

Mar.  15,  1919 

74.3 

1.4 

9.8 

82.7 

95.9 

63.9 

0.9 

'.370 

c?2911 

Blue 

2436 

2434 

Apr.  16,  1918 

74.0 

2  i 

1.8 

86.3 

98.0 

65.3 

1.0 

,000 

c?2912 

BlueG 

2436 

2434 

Do. 

74.6 

2.2 

1.8 

78.7 

93.2 

3.3 

0.2 

,200 

of  2919 

B 

2509 

2506 

Apr.  17.  1918 

1.5 

rf2935 

A 

2437 

2434 

Do. 

76.5 

2.1 

0.9 

86.3 

00.4 

6.9 

1.5 

^225 

c?2936 

Y 

2437 

2434 

Do. 

80.2 

0.6 

1.6 

85.1 

99.1 

6.0 

1.0 

,380 

0*2937 

StG 

2437 

2434 

Do. 

70.4 

1.4 

0.9 

77.9 

92.2 

2.8 

9.8 

,025 

o"2940 

A 

2430 

2434 

Do. 

68.9 

9.3 

0.4 

80.5 

91.0 

1.4 

0.6 

c?2941 

Y 

2430 

2434 

Do. 

68.5 

81.5 

95.7 

2.8 

0.2 

c?2980 

B 

2432 

2434 

Apr.  18,  1918 

77.0 

2.0 

2.5 

83.5 

97.4 

7.4 

0.8 

,315 

d"2981 

A 

2432 

2434 

Do. 

69.3 

9.3 

0.4 

88.0 

60.5 

9.5 

.910 

d"2998 

BlueG 

2511 

2506 

Apr.  19,  1918 

74.4 

1.4 

40.6 

80.8 

96.8 

65.0 

1.1 

.050 

0*2999 

StG 

2511 

2506 

Do. 

76.6 

1.6 

41.5 

83.3 

99.4 

66.0 

1.9 

,450 

tfSOOl 

G 

2576 

2506 

Do. 

11.7 

(73003 

B 

2576 

2506 

Do. 

3.7 

1  .1 

41.0 

78.8 

91.3 

62.7 

10.3 

2,035 

c?3005 

A 

2510 

2506 

Do. 

2.8 

l.< 

39.8 

75.1 

87.7 

61.5 

10.5 

1,900 

d"3006 

B 

2510 

2506 

Do. 

71.8 

41.4 

40.0 

76.3 

90. 

61.6 

10.0 

1,890 

0*3109 

B 

2474 

2473 

May    6,  1918 

71.1 

40.4 

39.0 

76.9 

90.9 

H.< 

10.4 

1.780 

c?3110 

B 

2474 

2473 

Do. 

70. 

39.9 

40.0 

76. 

89.3 

60.8 

10.5 

1,765 

d»3113 

A 

2474 

2473 

Do. 

67.0 

40.3 

38.9 

75.0 

86. 

57. 

10.2 

1,560 

d>3193 

StG 

2430 

2434 

June  14,  1918 

72.8 

40.0 

40. 

82.5 

95. 

64. 

10. 

1,880 

0"3194 

B 

2430 

2434 

Do. 

70.9 

40. 

39.9 

78.5 

88. 

61. 

10. 

2.020 

c73196 

Blue 

2430 

2434 

Do. 

75.0 

41.8 

40.6 

83. 

98. 

65. 

10. 

2.175 

d*3197 

G 

2576 

2506 

Do. 

74. 

42.5 

42.0 

80. 

94. 

63. 

10. 

2.250 

(73199 

B 

2576 

2506 

Do. 

74. 

42. 

42. 

78. 

90. 

62. 

10. 

2,080 

(73200 

A 

2576 

2506 

Do. 

73. 

41. 

40. 

78. 

89. 

62. 

10. 

1,930 

C73222 

B  An 

2432 

2434 

Do. 

78. 

41. 

42. 

84. 

100. 

66. 

11. 

2,160 

d*3239 

G 

2451 

2506 

June  15,  1918 

72. 

42. 

42. 

77. 

87. 

61. 

10. 

1,895 

0^3241 

StG 

2451 

2506 

Do. 

77. 

43. 

42. 

81. 

94. 

65. 

11. 

2,200 

<73298 

A 

2436 

2434 

June  16,  1918 

76. 

41. 

42. 

88. 

104. 

70. 

11. 

2.410 

cf3299 

A  An 

2436 

2434 

Do. 

72. 

41. 

10. 

80. 

95. 

65. 

10. 

1,790 

0*3300 

A 

2436 

2434 

Do. 

72. 

41. 

41. 

82. 

98. 

64. 

10. 

2.260 

(73302 

StG 

2436 

2434 

Do. 

75. 

41. 

41. 

81. 

93. 

64. 

10. 

2,260 

<73304 

StG 

2510 

2506 

June  17,  1918 

79. 

45. 

44. 

85. 

97. 

69. 

12. 

2.515 

(73367 

StG 

2437 

2434 

July  18,  1918 

73. 

41. 

40. 

83. 

99. 

63. 

11. 

2,280 

C73368 

G 

2437 

2434 

Do. 

75. 

42. 

43. 

84. 

100. 

67. 

10. 

2,390 

0*3396 

A 

2510 

2506 

July  23,  1918 

70. 

40 

40. 

82. 

95. 

65. 

10. 

c73398 

StG 

2510 

2506 

Do. 

72. 

42. 

43. 

79. 

93. 

64. 

11. 

2,125 

d*3391 

B 

2510 

2506 

Do. 

69. 

39. 

41. 

79. 

92. 

62. 

10. 

c73400 

StG 

2510 

2506 

Do. 

72. 

40. 

41. 

77. 

86. 

62. 

10. 

1,880 

<73420 

StG 

2474 

2473 

July     4,  1918 

69. 

39. 

39. 

76. 

89. 

61. 

9. 

1,760 

C73448 

StG 

2451 

2506 

Do. 

77. 

42. 

42. 

86. 

97. 

70. 

12. 

2,450 

0*3449 

G 

2451 

2506 

Do. 

74. 

42. 

41. 

80. 

92. 

65. 

10. 

2,180 

<73480 

G 

2576 

2506 

Do. 

74. 

41. 

41. 

79. 

92. 

61. 

10. 

2.125 

(7348 

B 

2576 

2506 

Do. 

74. 

42. 

41. 

78. 

90. 

61. 

10. 

1,975 

cf3529 

StG 

2511 

2506 

Do. 

71. 

40. 

40. 

80. 

92. 

64. 

10. 

2.130 

o"3533 

StG 

2511 

2506 

Do. 

73. 

40. 

41. 

82. 

95. 

66. 

11. 

2.300 

0*3534 

B 

2511 

2506 

Do. 

71. 

40. 

41. 

80. 

96. 

67. 

10. 

2,195 

GENETIC   STUDIES   OF  RABBITS  AND   RATS. 


49 


TABLE  33. — Descriptive  lift  of  rabbits  studied — Continued. 
VIII.     F2,  POLISH  X FLEMISH— Continued. 


Designa- 
tion. 

Color. 

Mother. 

Father. 

Born. 

Skull-length. 

Anterior 
skull-width.  1 

Posterior 
skull-width. 

J 

1 

a 

1 

i 
1 

^3603 

A  An 

2430 

2434 

Aug.    1,  1918 

75.0 

42.7 

41.6 

88.3 

101.9 

69.0 

11.7 

2.335 

d"3604 

B 

2430 

2434 

Do. 

76.3 

42.2 

41.7 

87.5 

100.5 

69.1 

11.4 

2.485 

c?3656 

A  An 

2436 

2434 

Nov.    2,  1918 

74.6 

41.2 

41.4 

83.8 

96.2 

64.6 

10.2 

2,110 

cT3660 

StG 

2436 

2434 

Do. 

71.1 

39.6 

40.7 

80.9 

93.5 

64.2 

9.6 

2.150 

d"3662 

A 

2432 

2434 

Do. 

79.9 

41.5 

42.4 

87.3 

101.2 

69.7 

12.1 

2,450 

d"3664 

Blue 

2432 

2434 

Do. 

71.7 

40.7 

41.3 

82.2 

96.8 

65.5 

9.9 

1,900 

c?3665 

B  An 

2432 

2434 

Do. 

77.8 

42.2 

41.9 

86.9 

102.2 

68.4 

10.9 

2.450 

d"3838 

StG 

2511 

2866 

Feb.  25,  1919 

67.9 

39.3 

40.8 

79.5 

93.5 

62.7 

10.3 

1,920 

cT3841 

G 

2451 

2866 

Feb.  27,  1919 

75.2 

41.0 

41.8 

75.7 

88.2 

58.8 

10.8 

1.645 

c?3849 

A 

2576 

2866 

Feb.  25,  1919 

68.9 

40.0 

41.0 

74.9 

88.4 

59.6 

9.8 

1.730 

d"3851 

B 

2576 

2866 

Do. 

70.7 

41.5 

40.1 

78.0 

91.1 

61.8 

10.4 

2.025 

cf3853 

BlueG 

2576 

2866 

Do. 

71.1 

41.4 

41.2 

78.7 

90.6 

61.2 

10.7 

1.870 

c?3859 

B 

2510 

2866 

Do. 

71.6 

39.9 

41.0 

79.0 

90.7 

60.5 

10.3 

1.850 

d"3878 

A 

2437 

2434 

Feb.  24,  1919 

72.0 

41.5 

41.8 

81.9 

98.1 

63.5 

10.3 

2.000 

cf3882 

G 

2509 

2866 

Feb.  25,  1919 

69.3 

40.8 

41.5 

78.9 

90.9 

64.3 

11.2 

1,970 

C"3889 

DilY 

2436 

2434 

Feb.  24,  1919 

73.5 

42.5 

42.8 

86.0 

99.5 

65.4 

10.7 

2,100 

d"4035 

StG 

2511 

2866 

May    5,  1919 

73.4 

39.6 

40.4 

78.1 

93.6 

63.4 

10.8 

2,010 

c?4037 

A 

2511 

2866 

Do. 

67.6 

38.2 

37.8 

71.3 

84.9 

56.3 

9.3 

1,675 

c?4066 

StG 

2436 

2433 

Do. 

70.3 

41.7 

40.8 

80.3 

95.4 

62.8 

9.8 

1.800 

c?4068 

YAn 

2432 

2434 

Mar.    3,  1919 

73.0 

40.8 

40.9 

85.2 

101.2 

66.3 

11.5 

1.920 

IX.   Fj,  HIMALA YAN  X FLEMISH. 


' 

_L 

1 

| 

Designa- 
tion. 

Color. 

. 

Born. 

1 

L 

J^. 

§ 

, 

1 

1 

3 

a! 

|| 

3 

Q 

;| 

§ 

H 

1? 

I 

t 

& 

3* 

I5 

& 

& 

1 

£ 

92983 

H 

2646 

2647 

Apr.  18,  1918 

74.6 

41.8 

41.5 

81.9 

93.9 

64.4 

10.8 

2,220 

92985 

G 

2646 

2647 

Do. 

78.8 

38.9 

40.4 

83.7 

96.4 

65.3 

12.3 

2,125 

92987 

B 

2646 

2647 

Do. 

80.8 

40.7 

41.0 

88.3 

101.4 

67.6 

11.9 

2,535 

92988 

B 

2646 

2647 

Do. 

76.5 

41.8 

41.8 

82.4 

94.7 

64.0 

11.3 

2,400 

93024 

B 

2517 

2522 

Apr.  20,  1918 

75.0 

41.8 

40.4 

84.7 

98.2 

68.4 

11.6 

2.675 

93025 

G 

2517 

2522 

Do. 

76.9 

41.8 

42.0 

82.9 

96.3 

66.1 

11.7 

2,900 

93026 

StG 

2517 

2522 

Do. 

73.0 

41.3 

42.8 

84.4 

96.7 

67.5 

12.2 

2.590 

93054 

G 

2521 

2522 

Apr.  22,  1918 

78.5 

40.1 

39.7 

84.4 

97.9 

66.6 

11.3 

2.160 

93149 

G 

2517 

2522 

June  14.  1918 

75.9 

41.5 

40.7 

82.9 

94.0 

66.8 

12.1 

2.680 

93150 

StG 

2517 

2522 

Do. 

76.0 

40.8 

41.7 

84.4 

94.9 

68.0 

12.0 

2,480 

93151 

StG 

2517 

2522 

Do. 

76.1 

42.6 

41.8 

87.3 

98.9 

69.7 

12.7 

2.380 

93153 

H 

2521 

2522 

Do. 

77.1 

41.4 

40.5 

88.8 

101.3 

71.4 

12.1 

2.705 

93157 

B 

2521 

2522 

Do. 

74.4 

41.5 

41.5 

83.9 

97.3 

67.4 

11.7 

2.290 

93202 

B 

2646 

2647 

Do. 

78.3 

41.9 

42.7 

81.9 

93.2 

64.0 

11.1 

2.440 

93228 

StG 

2645 

2647 

Do. 

77.5 

44.7 

43.4 

85.4 

97.0 

69.4 

12.0 

2,880 

93373 

G 

2519 

2522 

July  20,  1918 

75.4 

39.6 

39.6 

81.9 

95.7 

65.4 

11.7 

2.400 

93375 

G 

2519 

2522 

Do. 

77.2 

40.2 

40.8 

82.6 

93.0 

65.4 

11.3 

2.070 

93385 

G 

2642 

2647 

June  27.  1918 

77.3 

40.5 

40.5 

82.4 

95.9 

65.5 

11.0 

2.850 

93387 

StG 

2642 

2647 

Do. 

10.  S 

93389 

StG 

2642 

2647 

Do. 

74.4 

40.9 

41L3 

81A 

95.0 

ee's 

11.3 

2^520 

93439 

H 

2517 

2522 

Aug.  16,  1918 

76.8 

42.1 

42.2 

87.3 

99.6 

69.6 

11.1 

2.750 

93441 

StG 

2517 

2522 

Do. 

69.8 

38.9 

38.4 

79.2 

90.9 

63.1 

10   9 

2.260 

93442 

StG 

2517 

2522 

Do. 

75.9 

41.9 

40.4 

87.9 

100.5 

71.0 

11.8 

2.900 

50 


GENETIC   STUDIES   OF   RABBITS   AND   RATS. 


TABLE  33. — Descriptive  list  of  rabbits  studied — Continued. 
IX.   Ft,  HIM ALATANX  FLEMISH— Continued. 


DwiKn.i- 
tion. 

Color. 

| 

1 

Born. 

Skull-length. 

Anterior  skull-  1 
width. 

Posterior  skull-  1 
width. 

Femur. 

08 
3 

H 

Humerus. 

a 
W 

J3 
.» 

93443 

B 

2517 

2522 

Aug.  16,  1918 

79.1 

42.3 

42.9 

87.5 

101.0 

69.8 

12.6 

2,530 

93444 

8tG 

2517 

2522 

Do. 

73.3 

40.9 

41.9 

82.7 

93.8 

67.6 

11.1 

2,410 

93505 

G 

2645 

2647 

Do. 

76.1 

38.7 

40.7 

84.0 

95.6 

67.3 

11.0 

2.440 

93523 

G 

2521 

2522 

Do. 

78.0 

43.3 

41.7 

86.5 

99.1 

69.6 

11.5 

2,560 

93526 

G 

2521 

2522 

Do. 

74.0 

40.1 

40.8 

81.5 

92.5 

65.0 

11.0 

2,275 

93570 

G 

2830 

2647 

Aug.  21,  1918 

83.8 

45.3 

45.2 

89.0 

100.5 

69.2 

11  .8 

2.710 

93596 

G 

2646 

2647 

Sept.    1,  1918 

77.8 

42.8 

42.7 

87.3 

98.6 

67.3 

12.8 

2.750 

93600 

H 

2646 

2647 

Do. 

81.3 

43.5 

43.8 

89.5 

100.0 

69.7 

12.7 

2,990 

93601 

G 

2646 

2647 

Do. 

79.8 

42.7 

42.9 

88.7 

101.7 

70.8 

11.8 

2,620 

93647 

H 

2519 

2522 

Nov.    2,  1918 

74.2 

41.0 

42.4 

83.5 

95.5 

64.6 

11.6 

2,500 

(73023 

H 

2517 

2522 

Apr.  20,  1918 

12.1 

C73056 

G 

2521 

2522 

Apr.  22,  1918 

76!s 

41.2 

4l!i 

86.1 

99.5 

12.2 

(73057 

G 

2521 

2522 

Do. 

79.3 

41.7 

41.9 

85.1 

97.4 

66^3 

11.3 

(73145 

H 

2517 

2522 

June  14,  1918 

74.8 

41.0 

41.6 

84.6 

96.2 

67.3 

11.2 

2,185 

(73147 

StG 

2517 

2522 

Do. 

74.8 

42.2 

42.5 

88.4 

95.4 

67.5 

11.9 

2,170 

rf-3148 

StG 

2517 

2522 

Do. 

72.5 

41.9 

42.4 

82.6 

96.4 

67.7 

11.3 

2,190 

(73156 

G 

2521 

2522 

Do. 

73.8 

40.9 

41.2 

83.2 

96.5 

67.1 

10.8 

2.300 

C73158 

B 

2521 

2522 

Do. 

74.3 

41.3 

41.2 

81.2 

94.2 

64.9 

11.1 

2,300 

C73204 

G 

2646 

2647 

Do. 

76.6 

41.8 

42.5 

83.9 

97.4 

66.2 

12.0 

2,455 

(73206 

G 

2646 

2647 

Do. 

73.6 

42.8 

43.1 

78.9 

93.0 

63.1 

10.7 

2,450 

(73208 

G 

2646 

2647 

Do. 

73.1 

81.5 

96.6 

64.6 

11.1 

<73227 

StG 

2645 

2647 

Do. 

76.9 

43^4 

44.0 

83.7 

96.0 

66.4 

11.5 

2,480 

<73372 

H 

2519 

2522 

July  20,  1918 

84.9 

98.3 

67.7 

11.6 

2,350 

c73386 

StG 

2642 

2647 

June  27,  1918 

10.8 

C73388 

StG 

2642 

2647 

Do. 

10.8 

(73445 

StG 

2517 

2522 

Aug.  16,  1918 

75^7 

41.9 

42^6 

87.2 

106  'o 

70'2 

11.3 

2,470 

C73446 

B 

2517 

2522 

Do. 

78.0 

41.8 

41.5 

90.3 

102.8 

71.0 

12.1 

2,440 

c73496 

G 

2831 

2647 

Do. 

76.2 

43.4 

43.0 

86.7 

98.1 

70.7 

11.3 

2,555 

<73497 

G 

2831 

2647 

Do. 

77.0 

42.3 

42.7 

86.9 

99.9 

70.8 

10.9 

2,690 

(73503 

H 

2645 

2647 

Do. 

77.9 

42.1 

42.5 

82.9 

93.2 

64.6 

11.8 

2,460 

(73504 

H 

2645 

2647 

Do. 

77.8 

43.2 

44.0 

83.4 

95.8 

66.4 

11.0 

2,490 

(73506 

G 

2645 

2647 

Do. 

76.2 

40.6 

42.4 

80.3 

91.5 

62.7 

11.2 

2,430 

c73507 

G 

2645 

2647 

Do. 

77.6 

40.6 

42.6 

85.4 

95.5 

68.2 

12.0 

2,390 

(73508 

G 

2645 

2647 

Do. 

81.2 

44.2 

43.1 

88.8 

100.7 

69.8 

12.8 

2.740 

(73509 

StG 

2645 

2647 

Do. 

70.8 

40.4 

41.3 

80.8 

90.3 

64.9 

11.2 

2,190 

<73520 

B 

2521 

2522 

Do. 

70.4 

40.9 

40.0 

81.9 

95.6 

65.0 

10.6 

2.070 

(73524 

G 

2521 

2522 

Do. 

76.1 

40.4 

40.3 

86.0 

99.8 

67.2 

11.2 

2.170 

(73525 

G 

2521 

2522 

Do. 

76.3 

41.3 

41.6 

86.1 

98.9 

67.8 

11.4 

2.305 

(73568 

G 

2830 

2647 

Aug.  21,  1918 

80.3 

42.3 

42.7 

85.2 

98.1 

67.2 

11.1 

2.420 

(f8M9 

G 

2830 

2647 

Do. 

64.0 

10.6 

C73697 

G 

2646 

2647 

Sept.  1,  1918 

8CK3 

41.8 

42.6 

88.6 

101.6 

68.1 

11.6 

2.525 

4*8606 

G 

2646 

2647 

Do. 

79.9 

42.0 

43.2 

84.6 

98.7 

67.5 

12.0 

2.500 

(P85M 

G 

2646 

2647 

Do. 

80.3 

41.9 

44.7 

89.5 

101.9 

71.2 

12.0 

2,350 

c73602 

G 

2646 

2647 

Do. 

83.7 

44.0 

45.0 

89.7 

105.4 

71.5 

12.4 

2,870 

rf'SMI 

H 

2519 

2522 

Nov.    2,  1918 

73.0 

43.4 

43.0 

88.0 

99.8 

70.3 

12.3 

2,595 

i?M4i 

H 

2519 

2522 

Do. 

77.2 

43.9 

44.4 

89.4 

103.2 

69.8 

12.9 

2.640 

<73650 

G 

2519 

2522 

Do. 

71.9 

40.7 

40.9 

82.7 

99.1 

66.2 

11.6 

2.070 

PART  II, 

ON  A  NON-TRANSMISSIBLE  TRI-COLOR  VARIATION 

IN  RATS. 

In  the  course  of  studies  of  linkage  in  rats,  I  have  observed  the 
production  of  a  tri-color  individual,  gray,  yellow,  and  white,  similar 
to  the  tri-color  varieties  of  guinea-pig,  and  I  had  hoped  to  establish 
from  it  a  new  color  variety  of  rat,  but  thus  far  no  success  has  at- 
tended my  efforts.  The  case,  in  its  bearings  on  the  nature  and  origin 
of  variations,  is  not  without  interest,  and  so  will  be  described  briefly. 

The  two  genes  whose  linkage  relations  were  being  investigated 
when  the  tri-color  individual  made  its  appearance  have  been  desig- 
nated c  and  p.  Both  are  recessive  in  crosses  and  thus  become  visible 
as  somatic  characters  only  when  present  in  the  homozygous  state, 
cc  or  pp  respectively.  An  individual  of  the  formula  cc  is  an  albino; 
an  individual  of  the  formula  pp  is  pink-eyed  and  yellow-coated. 

When  an  ordinary  albino  is  crossed  with  a  pink-eyed  yellow  indi- 
vidual, young  are  produced  which  are  neither  albinos  nor  pink-eyed 
yellow,  since  neither  c  nor  p  will  be  homozygous  in  the  cross-bred 
individuals,  which  are  in  fact  gray  in  color  like  wild  rats,  or  else 
gray-hooded,  if  the  gene  for  hooded  pattern  is  present  in  homozygous 
condition.  By  means  of  such  crosses  between  albino  and  pink-eyed 
yellow  rats,  gray  and  gray-hooded  young  were  being  produced  when 
the  tri-color  individual  made  its  appearance.  It  is  a  gray-hooded 
individual,  like  its  brothers  and  sisters,  except  that  the  areas  nor- 
mally gray  are  liberally  mottled  with  yellow.  The  mottling  extends 
practically  throughout  the  colored  portions  of  the  coat  from  nose 
to  tail  tip.  The  yellow  areas  vary  in  size  from  those  which  contain 
merely  a  few  yellow  hairs  to  those  of  a  square  inch  in  extent.  The 
least  yellow  is  found  on  the  right  shoulder,  which  is  almost  like 
normal  gray  in  appearance.  The  most  yellow  is  found  in  the  middle 
of  the  back,  to  the  left  of  the  median  line,  where  a  large  spot  of 
clear  yellow  occurs  in  the  wide  back-stripe  of  the  hooded  pattern, 
which  would  correspond  roughly  with  grade  +2j/£  of  the  grading 
scale  used  in  our  studies  of  hooded  rats. 

The  tri-color  individual  is,  fortunately  for  the  purposes  of  genetic 
study,  a  male.  He  has  been  mated  with  albinos,  with  pink-eyed 
yellows,  and  with  gray  FI  cross-breds  between  the  albino  and  the 
pink-eyed  yellow  races,  and  later  with  his  own  daughters  of  the 
colors  white,  pink-eyed  yellow,  and  gray.  Hundreds  of  young  have 
been  produced  by  these  matings,  for  the  animal  is  a  remarkably 
large  and  vigorous  one  and  his  mates  have  proved  very  prolific,  but 

51 


52  GENETIC  STUDIES  OF  RABBITS  AND   RATS. 

not  one  of  the  young  was  mottled  like  the  sire.  This  occasioned  no 
surprise  when  the  mates  were  not  related  to  the  tri-color  male  or 
were  not  his  direct  descendants,  for  it  was  conjectured  that  he  might 
be  a  mutant  due  to  a  new  recessive  gene,  which  accordingly  would 
only  become  visible  when  in  a  homozygous  state.  But  if  he  him- 
self represented  such  a  homozygous  recessive  combination,  all  his 
gametes  should  transmit  the  mottled  condition,  and  all  his  daugh- 
ters consequently  should  be  heterozygous  for  the  mottled  condition, 
and  in  matings  with  their  sire  should  produce  50  per  cent  of  mottled 
individuals.  The  fact  that  they  do  not  produce  mottled  individuals 
shows  this  hypothesis  to  be  untenable. 

The  tri-color  male,  in  fact,  breeds  like  his  gray-hooded  brothers 
and  sisters,  producing  gametes  which  are  commonly  either  c  or  p, 
but  which  in  no  case  transmit  a  mosaic  relationship.  From  his 
ancestry  and  from  the  results  of  his  matings,  we  know  him  to  be  a 
double  heterozygote,  CcPp.  The  Mendelian  expectation  is  that  he 
will  form  four  kinds  of  gametes,  cP,  Cp,  CP,  and  cp,  but  since  there 
exists  linkage  (in  this  case  repulsion)  between  c  and  p,  the  first  two 
classes  of  gametes  will  be  commoner  than  the  other  two.  His 
breeding  behavior  accords  with  these  expectations.  In  most  of  his 
gametes  he  transmits  either  albinism  or  pink-eyed  yellow.  In  an 
occasional  gamete  he  probably  transmits  both,  a  matter  which  has 
not  been  tested,  as  it  would  require  special  matings.  It  is  certain 
that  in  an  occasional  gamete  he  transmits  neither  c  nor  p,  a  condition 
expressed  hi  the  formula  CP,  which  like  cp  would  represent  a  cross- 
over. His  gametes,  accordingly,  appear  to  be  such  as  are  normally 
produced  by  Fi  doubly  heterozygous  individuals  like  his  gray  and 
gray-hooded  brothers  and  sisters. 

How,  then,  can  we  account  for  the  production  of  yellow  areas  in 
the  gray  coat?  By  an  explanation  similar  to  that  which  Morgan 
and  Bridges  (19191)  have  given  to  account  for  the  production  of 
gynandromorphs  in  Drosophila.  We  may  suppose  that  at  an  early 
cleavage  (perhaps  the  first)  of  the  fertilized  egg  from  which  this  rat 
developed,  one  of  the  pair  of  chromosomes,  in  which  the  genes  c 
and  p  are  borne,  failed  to  divide  as  normally,  or  that  for  some  other 
reason  it  failed  to  pass  into  one  of  the  cell-products.  Further  con- 
sideration shows  that  it  must  have  been  the  maternal  rather  than 
the  paternal  chromosome  of  this  pair  which  was  lost.  For  the  mother 
was  an  albino  and  must  have  contributed  cP,  but  the  father  was  a 
pink-eyed  yellow,  Cp,  and  his  contribution  by  itself  would  produce 
yellow  fur,  whereas  with  the  mother's  contribution  it  would  pro- 
duce gray.  We  may  suppose,  accordingly,  that  a  blastomere  con- 
taining only  the  paternal  contribution  produced  that  part  of  the 

>  Carnegie  Inat.  Wash.  Pub.  No.  278. 


GENETIC   STUDIES   OF   RABBITS   AND    RATS.  53 

skin  which  is  yellow,  and  that  a  blastomere  or  blastomeres  contain- 
ing as  normally  both  maternal  and  paternal  members  of  this  chromo- 
some pair  produced  the  gray  part  of  the  coat. 

But  how  about  the  germ-cells  of  this  individual?  Does  the  mixed 
condition  seen  in  the  coat  obtain  also  among  the  germ-cells?  Very 
likely  it  does.  But  if  so,  no  tri-color  progeny  need  be  expected  in 
consequence.  For  those  germ-cells  which  correspond  in  composition 
with  the  gray  parts  of  the  coat  would  produce  gametes  like  those  of 
any  other  FI  individual,  which  for  the  most  part  would  transmit 
either  albinism  or  pink-eyed  yellow,  with  an  occasional  gamete 
transmitting  gray  and  an  occasional  gamete  transmitting  both  albin- 
ism and  pink-eyed  yellow.  But  the  germ-cells  corresponding  to 
the  yellow  parts  of  the  coat  would  transmit  either  pink-eyed  yellow 
or  nothing  (so  far  as  the  chromosome  under  discussion  is  concerned). 
It  is  an  open  question  whether  this  last  type  of  gamete  (lacking  the 
entire  chromosome)  would  be  viable,  and  if  it  were,  its  existence  would 
be  difficult  to  detect,  since  it  would  behave  like  the  double  recessive 
type  of  gamete,  cp,  in  its  effects  on  coat  color. 

How,  then,  could  a  genuine  genetically  transmissible  type  of 
mottled  rat  arise?  Only,  I  suppose,  by  a  change  in  the  genetic 
locus  at  P,  p,  so  that  it  became,  instead  of  P  alone  or  p  alone,  a 
mosaic  Pp  transmissible  as  a  unit  and  capable  of  functioning  as  the 
allelomorph  either  of  P  or  of  p.  Such  apparently  is  the  case  in  the 
guinea-pig,  where  Ibsen  has  shown  the  mottled  condition  to  be  the 
allelomorph  of  both  simple  black  and  simple  yellow.  Such  appar- 
ently is  also  the  condition  in  the  mottled  variety  of  rabbit  called 
"Japanese,"  which  I  have  recently  studied  in  a  series  of  crosses,  and 
such  would  appear  to  be  the  case  in  maize  with  striped  pericarp, 
which  has  been  extensively  studied  by  Emerson  and  his  associates. 
They  find  that  the  mosaic  factor  frequently  becomes  simple  by 
mutation  either  to  all  red  or  to  all  white,  and  that  mutation  occurs 
oftenest  to  that  component  of  the  mosaic  which  is  most  extensive 
in  the  parent.  This  result  is  easily  understood  if  we  suppose  that 
the  mosaic  "gene"  divides  in  such  a  way  as  to  include  more  of  one 
of  its  components  than  of  the  other  in  a  cell  product,  or  so  as  to 
contain  only  the  major  component  in  a  cell  product.  That  cell 
would  then  develop  into  a  self-colored  individual.  I  think  that 
this  idea  of  a  mosaic  gene  will  explain  the  high  degree  of  variability 
which  is  found  not  only  in  striped  maize,  but  also  in  spotted  mam- 
mals, whether  spotted  with  yellow  or  with  white.  Hooded  rats  and 
Dutch  rabbits  are  examples  of  spotted  mammals  which  I  have  stud- 
ied extensively  and  have  found  to  be  amenable  to  selection  like  the 
striped  pericarp  of  maize  studied  by  Emerson  and  by  Hays,  probably 
for  the  same  reason,  viz,  because  a  mosaic  gene  varies  (or,  if  you 
prefer,  "mutates")  in  the  proportions  of  its  constituents. 


54  GENETIC   STUDIES   OF   RABBITS   AND   RATS. 

In  19121  I  described  a  peculiar  guinea-pig,  which,  in  the  light  of 
the  present  case,  I  am  inclined  to  explain  in  the  same  way  as  the 
tri-color  rat,  as  a  non-transmissible  though  not  of  necessity  a  purely 
somatic  mutation.  At  that  time  I  characterized  the  guinea-pig  in 
question  as  a  "pink-eyed  individual  with  a  colored  coat,"  but  this 
is  not  a  very  good  description  for  it.  The  description  fits  better  a 
genuine  genetically  transmissible  variety  that  was  then  unknown  to 
us,  but  which  curiously  enough  was  soon  to  appear  in  our  breeding- 
pens  from  stock  that  had  recently  been  obtained  in  Peru.  The  indi- 
vidual, whose  peculiarities  were  not  transmitted  to  its  offspring, 
was  by  pedigree  a  heterozygote  between  albinism  and  pale  black. 
Such  a  heterozygote  I  believe  it  in  fact  to  have  been,  but  in  appearance 
it  was  white,  except  for  some  small  spots  of  pale  black  ("blue")  on 
the  right  side  of  the  head  and  on  the  hips.  The  head  pigmentation 
extended  as  a  "faint  pigmented  streak"  on  to  "the  iris  of  each 
eye."  The  mother  of  this  animal  was  blue,  the  father  cream  (which 
is  recessive  to  blue),  but  he  also  transmitted  albinism.  He  can  not 
have  transmitted  blue,  since  that  is  dominant  to  cream.  Undoubt- 
edly, then,  the  egg  from  which  this  individual  developed  transmitted 
color  (C)  and  blue  (E)  which  lie  in  different  chromosomes.  But 
the  father  transmitted  albinism  (c)  and  cream  (e),  which  are  reces- 
sive allelomorphs  of  C  and  E  respectively.  Evidently  it  was  the 
maternal  chromosome  bearing  C  which  was  lost  from  the  greater 
part  of  the  ectoderm  of  the  embryo,  since  no  other  loss  would  have 
produced  an  uncolored  coat  and  eye.  Whether  or  not  E  was  lost 
in  the  same  regions  can  not  be  determined,  but  since  all  colored 
areas  were  blue,  not  cream,  it  is  evident  that  wherever  C  was  re- 
tained, E  was  retained  also. 

The  peculiar  individual  was  a  female  and  produced  three  young, 
all  albinos  as  I  recall,  by  an  albino  sire,  before  her  untimely  death. 
It  can  not  be  stated,  therefore,  whether  the  germ-cells  were  hetero- 
zygous in  nature  or  were  like  the  greater  part  of  the  coat,  pure  albino, 
inherited  from  the  sire  alone.  Certainly  none  of  the  three  develop- 
ing ova  transmitted  the  mosaic  condition  found  in  the  mother.  It 
seems  probable,  though  it  is  regrettably  unverifiable,  that  no  young 
mottled  like  the  mother  would  have  been  obtained,  had  we  been 
able  to  obtain  a  much  larger  number  of  young. 

1  Science.  36,  p.  508. 


BIBLIOGRAPHY. 


CASTLE,  W.  E.     1914.     The  nature  of  size  factors  as  indicated  by  a  study  of  correlation. 

Carnegie  Inst.  Wash.  Pub.  No.  196,  pp.  51-55. 
— .     1921.     On  a  method  of  estimating  the  number  of  genetic  factors  concerned  in 

cases  of  blending  inheritance.     Science,  54,  pp.  93-96,  223. 
—  in  collaboration  with  H.  E.  WALTER,  R.  C.  MULLENIX,  and  S.  COBB.     1909.     Studies 

of  inheritance  in  rabbits.     Carnegie  Inst.  Wash.  Pub.  No.  114,  70  pp.,  4  pi. 
DAVENPORT,  C.  B.     1917.     Inheritance  of  stature.     Genetics,  2,  313-389. 
GALTON,  F.     1889.     Natural  inheritance.     259  pp. 
HARVEY,  ETHEL  B.     1920.     A  review  of  the  chromosome  numbers  in  the  metazoa  II. 

Jour.  Morph.,  34,  1-68. 
HOSHINO,  Y.     1915.     On  the  inheritance  of  the  flowering  time  in  peas  and  rice.     Jour. 

Col.  Agr.,  Tohoku  Imp.  Univ.,  6. 
LANG,  A.     1910.     Die  Erblichkeitsverhaltnisse  der  Ohrenlange  der  Kaninchen,  etc.     Zeit.  f. 

ind.  Abst.  u.  Vererbungslehre,  4,  1-23. 
MACDOWELL,   E.   C.     1914.     Size  inheritance  in  rabbits.     Carnegie  Inst.  Wash.  Pub. 

No.  196,  pp.  1-49,  9  figs. 
MILLER,  G.  S.     1912.     Catalogue  of  the  mammals  of  Western  Europe.     1019  pp.     British 

Museum,  London. 
PUNNETT,  R.  C.     1912.     Inheritance  of  coat-colour  in  rabbits.    Jour.  Genetics,  2,  pp. 

221-238,  pi.  12-14. 
and  P.  G.  BAILEY.     1914.     On  inheritance  of  weight  in  poultry.     Jour.  Genetics, 

4,  23-39,  pi.  IV. 
-.     1915.     Further  experiments  on  the  inheritance  of  coat-colour  in  rabbits.     Jour. 

Genetics,  5,  pp.  37-50. 
.     1918.     Genetic   studies   in   rabbits.     I.  On  the  inheritance  of  weight.    Jour. 

Genetics  8,  1-25. 
WRIGHT,  SEWALL.     1918.     On  the  nature  of  size  factors    Genetics,  3,  367-374. 

55 


PLATE   1 


P,  Polish  9~2,  mother  of  F,  yonm: 
//,  Himalayan  91,  mother  of  FI  yi 
/•',  Flemish  (lianl  V  7,  color  steel  u 
The  relative  si/.e  is  ronerllv  >ho\\: 


•oosefl  with  hotli  the  uther  races. 
in  en.— r-  \vitli  Imth  the  other  races 
mother  of  FI  young  bv  a  Polish  sire. 
:cent  in   the  case  of  the    Polish  in- 


PLATE  2 


Skull  and  certain  leg  Ixines  of  representative  individuals  of  the  three  pure  races  of  i.-il.liiis 
and  of  their  Fj  hybrids,  shown  on  the  same  scale  of  reduction  in  size.  To  the  left  of  the  skull 
of  each  rabbit  is  seen  the  tibia-fibula,  and  to  the  right  of  the  skull  the  femur  of  the  ri^ht  hind- 
leg.  Below  the  skull  is  seen  the  right  humerus. 

P,  bones  of  Polish  9  9.  F,  bones  of  Flemish  97,  shown  alive  in  plate  1,  /•'.  //,  Uu,-  ..i 
Himalayan  96.  Fu  P  X  F,  l>ones  of  92436,  daughter  of  Flemish  97  and  of  Polish  o"3.  F,, 
P  X  H,  bones  of  92320,  daughter  of  Polish  99  and  of  Himalayan  c?5.  FI,  H  X  F.  Inn,.-  ..f 
92431,  daughter  of  Himalayan  90  and  Flemish  cT2. 


431 


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